mesa: Fix a case when gbm is enabled but DRIDRIVERS is not defined

This is a typical scenario with arm platforms, with meson if DRIDRIVERS
is empty then dri is disabled automatically, but gbm needs dri2 enabled
for it to have proper backend, in autotools we could use --enable-gbm
--enable-dri and get correct behaviour but with meson enabling dri2 only
works if DRIDRIVERS is not empty

This fixes mesa-gl build for rpi machines when using userland graphics

(From OE-Core rev: 0c670a0fad379c3dc2a69ac5abfeaceda98a2f9c)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-graphics/mesa/files/0001-Allow-enable-DRI-without-DRI-drivers.patch

@@ -0,0 +1,45 @@
+From 8e0a58c8eea7ed70071cac139655700fdfa16445 Mon Sep 17 00:00:00 2001
+From: Andrei Gherzan <andrei@gherzan.ro>
+Date: Wed, 22 May 2019 18:32:07 +0100
+Subject: [PATCH] Allow enable DRI without DRI drivers
+
+Upstream-status: Pending
+Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>
+---
+ meson.build       | 2 +-
+ meson_options.txt | 6 ++++++
+ 2 files changed, 7 insertions(+), 1 deletion(-)
+
+diff --git a/meson.build b/meson.build
+index 53d02e3..9a8578f 100644
+--- a/meson.build
++++ b/meson.build
+@@ -119,7 +119,7 @@ with_dri_r200 = _drivers.contains('r200')
+ with_dri_nouveau = _drivers.contains('nouveau')
+ with_dri_swrast = _drivers.contains('swrast')
+ 
+-with_dri = _drivers.length() != 0 and _drivers != ['']
++with_dri = get_option('dri') or (_drivers.length() != 0 and _drivers != [''])
+ 
+ _drivers = get_option('gallium-drivers')
+ if _drivers.contains('auto')
+diff --git a/meson_options.txt b/meson_options.txt
+index ccf7065..5174320 100644
+--- a/meson_options.txt
++++ b/meson_options.txt
+@@ -34,6 +34,12 @@ option(
+   choices : ['auto', 'true', 'false'],
+   description : 'enable support for dri3'
+ )
++option(
++  'dri',
++  type : 'boolean',
++  value : false,
++  description : 'enable support for dri'
++)
+ option(
+   'dri-drivers',
+   type : 'array',
+-- 
+2.17.1
+

meta/recipes-graphics/mesa/mesa.inc

@@ -70,7 +70,7 @@ DRIDRIVERS_class-nativesdk = "swrast"
 DRIDRIVERS_append_x86_class-target = ",r100,r200,nouveau,i965,i915"
 DRIDRIVERS_append_x86-64_class-target = ",r100,r200,nouveau,i965,i915"
 # "dri" requires "opengl"
-PACKAGECONFIG[dri] = "-Ddri-drivers=${DRIDRIVERS}, -Ddri-drivers='', xorgproto libdrm"
+PACKAGECONFIG[dri] = "-Ddri=true -Ddri-drivers=${DRIDRIVERS}, -Ddri=false -Ddri-drivers='', xorgproto libdrm"
 PACKAGECONFIG[dri3] = "-Ddri3=true, -Ddri3=false, xorgproto libxshmfence"
 
 # Vulkan drivers need dri3 enabled

meta/recipes-graphics/mesa/mesa_19.0.3.bb

@@ -3,6 +3,7 @@ require ${BPN}.inc
 SRC_URI = "https://mesa.freedesktop.org/archive/mesa-${PV}.tar.xz \
            file://0001-meson.build-check-for-all-linux-host_os-combinations.patch \
            file://0001-meson.build-make-TLS-GLX-optional-again.patch \
+           file://0001-Allow-enable-DRI-without-DRI-drivers.patch \
            "
 
 SRC_URI[md5sum] = "d03bf14e42c0e54ebae5730712ccc408"