kernel: mmu: fix bitmap set and clear under direct map

When CONFIG_KERNEL_DIRECT_MAP enabled, the region to be mapped
or unmapped can be outside of the virtual memory space, wholly
within it, or overlap partially. Additional processing is
needed to make sure we only manipulate the bits within
the bitmap, in other words, only the pages represented by
the bitmap.

Fixes #59549

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