MMU: allow page-table loads/stores if MMU is off

[FioraAeterna]

Fixes regressions in some games that apparently required this to work, but
don't really require full MMU emulation (e.g. with exceptions and all).

[FioraAeterna]

Attempt at an explanation: the patch that disabled MMU loads in non-MMU mode treated MMU as equivalent to "page table support". But some games use page tables but don't need full MMU mode (e.g. F-Zero GX) because they don't need the full exception support and all that jazz. So we want to let them still use the MMU path; otherwise we'd have to enable the full MMU mode for those games even though they don't need it.

[phire]

Ok, The Enable MMU option is badly misnamed.

It has nothing to do with MMU and really should be renamed something like "Enable Data Exceptions"