arm64: mm: Use asid feature macro for cheanup

The commit 95b54c3e

 ("KVM: arm64: Add feature register flag
definitions") introduce the ID_AA64MMFR0_ASID_8 and ID_AA64MMFR0_ASID_16
macros.

We can use these macros for cheanup in get_cpu_asid_bits().

No functional change.

Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/f71c75d3-735e-b32a-8414-b3e513c77240@huawei.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>