tests: mem_protect/mem_map: skip z_phys_map when linking in virt

When the kernel links in virtual address space, the data
structures needed for the z_phys_map() no longer point to physical
addresses (which are required for z_phys_map() to work). So skips
these tests if CONFIG_KERNEL_LINK_IN_VIRT=y.

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