arm/edk2-firmware: explicitly set level of parallelisation

Explicitly set the level of parallelisation instead of letting build.sh
determine it.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm/recipes-bsp/uefi/edk2-firmware.inc

@@ -98,6 +98,7 @@ do_compile() {
        --buildtarget ${EDK2_BUILD_MODE} \
        --tagname ${EDK_COMPILER} \
        --platform ${EDK2_PLATFORM_DSC} \
+       ${@oe.utils.parallel_make_argument(d, "-n %d")} \
        ${EDK2_EXTRA_BUILD}
 }