tests: mem_protect/mem_protect: more tables for QEMU Cortex A53

For qemu_cortex_a53 on the mem_protect test, the test
test_mem_domain_init_fail() fails due to not having enough
translation tables. However, since ARM64 MMU asserts on such
condition, and k_mem_domain_init() also asserts when fails,
there is no way to distinguish these two assertions at runtime,
thus the test was considered passing. Fix this by allocating
a few more tables so the test will actually fail on
k_mem_domain_init().

Signed-off-by: Daniel Leung <daniel.leung@intel.com>