sh: Simplify phys_addr_mask()/PTE_PHYS_MASK for 29/32-bit.

Given that __in_29bit_mode() is a constant for the non-PMB case, we can
simply use the PMB-facing version of phys_addr_mask() and drop the other
variants.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>