add support for power8 to xcompile script

power8 is set up by ibm as a powerpc subset, so we follow
that rule here: we call it a powerpc but require -mcpu=power8

Change-Id: Ib5212be22db9584b0dc0eeed5c06ec1924347067
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://review.coreboot.org/12624
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/xcompile/xcompile

@@ -231,7 +231,7 @@ EOF
 }
 
 # Architecture definitions
-SUPPORTED_ARCHITECTURES="arm arm64 mipsel riscv x64 x86"
+SUPPORTED_ARCHITECTURES="arm arm64 mipsel riscv x64 x86 power8"
 
 arch_config_arm() {
 	TARCH="arm"
@@ -286,6 +286,16 @@ arch_config_mipsel() {
 	TENDIAN="EL"
 }
 
+arch_config_power8() {
+	TARCH="powerpc"
+	TBFDARCHS="powerpc"
+	TCLIST="powerpc"
+	TWIDTH="64"
+	TSUPP="power8"
+	TABI="elf"
+	CC_RT_EXTRA_GCC="-mcpu=power8"
+}
+
 test_architecture() {
 	local architecture=$1
 	local endian gccprefix search