arm64: don't trash config with compat symbol if COMPAT is disabled

ARCH_WANT_COMPAT_IPC_PARSE_VERSION is selected unconditionally. It
makes little sense if kernel is compiled without COMPAT support.
Fix it.

This patch makes no functional changes since all existing code which
is guarded with ARCH_WANT_COMPAT_IPC_PARSE_VERSION is also guarded
with COMPAT.

Signed-off-by: Yury Norov <ynorov@marvell.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>