arm: armv8: remove redundant definition of mmu_status
mmu_status is used in io memcpy functions to prevent accesses to non
8-byte aligned addresses when the mmu is disabled. Though there is a
redundant definition enabled when icaches is turned off by setting
SYS_ICACHE_OFF.
This patch removes the redundant definition, allowing mmu_status to
properly report the status regardless of config settings. This shouldn't
be a problem since access to non 8-byte aligned data can be done
irrespective of icache state.