selftests/mm: va_high_addr_switch: dynamically initialize testcases to enable LPA2 testing

Post FEAT_LPA2, the Aarch64 Linux kernel extends higher address support to
4K and 16K translation granules.  To support testing this out, we need to
do away with static initialization of page size, while still maintaining
the nice array of testcases; this can be achieved by initializing and
populating the array as a stack variable, and filling in the page size and
hugepage size at runtime.

Link: https://lkml.kernel.org/r/20240522070435.773918-3-dev.jain@arm.comSigned-off-by: Dev Jain <dev.jain@arm.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>