boot/edk2: add a new Kconfig option to pass arbitrary build options

EDK2 build may include extra options. Those are usually in the form
of "-D SOMEFLAG_ENABLE" and might be specific for a processor
architecture or a platform. For example:
"-D NETWORK_HTTP_BOOT_ENABLE", "-D NETWORK_TLS_ENABLE", ...

Those options are generally documented in their respective packages.
See for example:
https://github.com/tianocore/edk2/blob/master/OvmfPkg/README

This commit adds a new Kconfig string option to let the use define
arbitrary build flags.

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

boot/edk2/Config.in

@@ -130,6 +130,21 @@ config BR2_TARGET_EDK2_OVMF_DEBUG_ON_SERIAL
 	  See OVMF README:
 	  https://github.com/tianocore/edk2/blob/master/OvmfPkg/README
 
+config BR2_TARGET_EDK2_EXTRA_BUILD_OPTS
+	string "Extra build options"
+	help
+	  EDK2 build may include extra options. Those are usually in
+	  the form of "-D SOMEFLAG_ENABLE" and might be specific for a
+	  processor architecture or a platform. For example: "-D
+	  NETWORK_HTTP_BOOT_ENABLE", "-D NETWORK_TLS_ENABLE", ...
+
+	  Those options are generally documented in their respective
+	  packages. See for example:
+	  https://github.com/tianocore/edk2/blob/master/OvmfPkg/README
+
+	  This configuration is an arbitrary string that will be
+	  passed to the build command.
+
 config BR2_TARGET_EDK2_FD_NAME
 	string
 	default "OVMF" if BR2_TARGET_EDK2_PLATFORM_OVMF_I386

boot/edk2/edk2.mk

@@ -156,7 +156,8 @@ EDK2_BUILD_OPTS += \
 	-n $(BR2_JLEVEL) \
 	-a $(EDK2_ARCH) \
 	-b $(EDK2_BUILD_TYPE) \
-	-p $(EDK2_PACKAGE_NAME)/$(EDK2_PLATFORM_NAME).dsc
+	-p $(EDK2_PACKAGE_NAME)/$(EDK2_PLATFORM_NAME).dsc \
+	$(call qstrip,$(BR2_TARGET_EDK2_EXTRA_BUILD_OPTS))
 
 define EDK2_BUILD_CMDS
 	mkdir -p $(EDK2_BUILD_PACKAGES)