selftests/mm: rename va_128TBswitch to va_high_addr_switch

As the initial selftest only took into consideration PowperPC and x86
architectures, on adding support for arm64, a platform independent naming
convention is chosen.

Link: https://lkml.kernel.org/r/20230323105243.2807166-3-chaitanyas.prakash@arm.com


Signed-off-by: Chaitanya S Prakash <chaitanyas.prakash@arm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>