armv8/tunes: Set TUNE_PKGARCH_64 based on ARMPKGARCH

armv8/tunes: Set TUNE_PKGARCH_64 based on ARMPKGARCH

The setting is to modify TUNE_PKGARCH which is filled with
TUNE_PKGARCH_64 or TUNE_PKGARCH_32 in arm-arch64.inc
This lets higher up tune files for arm64 SOCs override them if needed,
this can help building multiple armv8 machines with different tunes in
same workspace.

No need to set TUNE_PKGARCH in tune files as it is synthesized from ARMPKGARCH

Add ARMPKGARCH for aarch64 tunes

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>