Introduce initial implementation of the ARMv6/v7 superpages management routines

Implemented basic promotion, demotion, enter and remove mechanisms for 1MB
superpages along with related PV entry management.
Prepare structures, macros and sysctls to be used by superpages.
Change existing L1 descriptors management to be able to process both L1 page
directories and L1 page table entries.
Enable compilation of the newly created routines by creating a dummy
calls - to be removed when proper utilization is implemented.
Introduce preliminary superpages for ARMv6/v7 support.

Implement missing functions, modify pmap API, fix noticed bugs.