ppc: io.h: Use addrmap_ translation APIs only in post-relocation phase

ppc: io.h: Use addrmap_ translation APIs only in post-relocation phase

In phys_to_virt() and virt_to_phys(), if CONFIG_ADDR_MAP is defined,
they use addrmap_ translation APIs to do the address translation.
However these APIs only work in post-relocation phase.

Update the code logic to fall back to use the default one when in
pre-relocation phase.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>