arm-bsp/sbsa-ref: add e1000e to kernel config

Recent changes to the arm64 kernel defconfig changed CONFIG_E1000E from
built-in to a module. This breaks testimage networking on the SBSA
Reference platform.

testimage provides the target network configuration through the kernel
“ip=” command-line option. The kernel needs the network driver to be
built-in in order to configure the interface from this option during
boot. With e1000e built as a module, the interface is not available at
that point and testimage is unable to establish an SSH connection to the
target.

Set CONFIG_E1000E=y in the sbsa-ref kernel configuration to make the
driver built-in again and restore testimage SSH testing.

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

meta-arm-bsp/recipes-kernel/linux/files/sbsa-ref/e1000.cfg

@@ -0,0 +1 @@
+CONFIG_E1000E=y

meta-arm-bsp/recipes-kernel/linux/linux-arm-platforms.inc

@@ -135,3 +135,6 @@ KBUILD_DEFCONFIG:sbsa-ref = "defconfig"
 KCONFIG_MODE:sbsa-ref = "--alldefconfig"
 # Upstream defconfig often causes warnings but we don't maintain it
 KCONF_BSP_AUDIT_LEVEL:sbsa-ref = "0"
+# Build e1000e into the kernel for testimage
+FILESEXTRAPATHS:prepend:sbsa-ref := "${ARMBSPFILESPATHS}"
+SRC_URI:append:sbsa-ref = " file://e1000.cfg"