selftests: riscv: Allow mmap test to compile on 32-bit

Macros needed for 32-bit compilations were hidden behind 64-bit riscv
ifdefs. Fix the 32-bit compilations by moving macros to allow the
memory_layout test to run on 32-bit.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Fixes: 73d05262 ("selftests: riscv: Generalize mm selftests")
Link: https://lore.kernel.org/r/20240808-mmap_tests__fixes-v1-1-b1344b642a84@rivosinc.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>