UefiCpuPkg/CpuMmuLib: Adjust default memory attributes on LoongArch

When updating memory attributes, if only access attributes are changed,
the default memory cache attribute is NULL and a CACHE_CC is added by
default.

Signed-off-by: Chao Li <lichao@loongson.cn>

UefiCpuPkg/Library/CpuMmuLib/LoongArch64/CpuMmu.c

@@ -595,6 +595,7 @@ EfiAttributeConverse (
       LoongArchAttributes &= ~PAGE_DIRTY;
       break;
     default:
+      LoongArchAttributes |= CACHE_CC;
       break;
   }