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.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/context.c

@@ -50,10 +50,10 @@ static u32 get_cpu_asid_bits(void)
 		pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n",
 					smp_processor_id(),  fld);
 		fallthrough;
-	case 0:
+	case ID_AA64MMFR0_ASID_8:
 		asid = 8;
 		break;
-	case 2:
+	case ID_AA64MMFR0_ASID_16:
 		asid = 16;
 	}