arm-bsp/juno: use virtual/bootloader for u-boot/edk2

To setup juno to use either u-boot or edk2 in CI, abstract out the
relevant parts and setup the parts to allow for it to be done
dynamically.

Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm-bsp/conf/machine/juno.conf

@@ -19,8 +19,9 @@ SERIAL_CONSOLES = "115200;ttyAMA0"
 
 PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
 PREFERRED_VERSION_u-boot ?= "2020.07"
+PREFERRED_PROVIDER_virtual/bootloader ?= "u-boot"
 
-EXTRA_IMAGEDEPENDS += "trusted-firmware-a edk2-firmware u-boot firmware-image-juno"
+EXTRA_IMAGEDEPENDS += "trusted-firmware-a virtual/bootloader firmware-image-juno"
 
 # Juno u-boot configuration
 UBOOT_MACHINE = "vexpress_aemv8a_juno_defconfig"

meta-arm-bsp/recipes-bsp/trusted-firmware-a/trusted-firmware-a-juno.inc

@@ -4,7 +4,7 @@ COMPATIBLE_MACHINE = "juno"
 TFA_PLATFORM = "juno"
 TFA_DEBUG = "1"
 TFA_MBEDTLS = "1"
-TFA_UBOOT = "1"
+TFA_UBOOT ?= "1"
 TFA_BUILD_TARGET = "bl1 bl2 bl31 dtbs fip"
 
 # Juno needs the System Control Processor Firmware