xtensa: mmu: no need to ignore array bound for SoC MMU ranges

The #pragma to ignore array bounds for xtensa_soc_mmu_ranges[]
was a remnant before code refactoring during review. Since
this array is no longer declared __weak and as a zero length
array, the #pragma to ignore array bounds is no longer needed.
So remove them.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>