cortex-a8: more MMU support

cortex-a8: more MMU support

+ virt2phys() can now convert virtual address to real
+ read_memory() and write_memory() are renamed to read_phys_memory()
and write_phys_memory()
+ new read_memory() and write_memory() try to resolve real address if
mmu is enambled than perform real address reading/writing
   + if address is bellow 0xc000000 than TTB0 is used for page table
dereference, if above - than TTB1. Linux style of user/kernel address
separation
   + if above fails (i.e address is unspecified) than mode is checked
whether it is Supervisor (than TTB1) or User (than TTB0)
- Software breakpoints doesn't work. You should invoke
"gdb_breakpoint_override hard" before you start debugging
+ cortex_a8_mmu(), cortex_a8_enable_mmu_caches(),
cortex_a8_disable_mmu_caches() are implemented

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>