arch-arm64.inc: Lower the priority of aarch64 in MACHINEOVERRIDES

This makes sure, e.g., ${SOC_FAMILY} and ${MACHINE} have higher
priorities than aarch64.

(From OE-Core rev: 3b8db95973fc144b00d59c4797adb405a935cd7c)

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/conf/machine/include/arm/arch-arm64.inc

@@ -4,7 +4,7 @@ require conf/machine/include/arm/arch-armv7ve.inc
 
 TUNEVALID[aarch64] = "Enable instructions for aarch64"
 
-MACHINEOVERRIDES .= "${@bb.utils.contains('TUNE_FEATURES', 'aarch64', ':aarch64', '' ,d)}"
+MACHINEOVERRIDES =. "${@bb.utils.contains('TUNE_FEATURES', 'aarch64', 'aarch64:', '' ,d)}"
 
 # Little Endian base configs
 AVAILTUNES += "aarch64 aarch64_be"