ARM: fix bootloader's mmu_map_physical_memory size

When the address is not page aligned, not only adjust the address
to start mapping, but also take the "overflow" on the last page
into account.

This makes the bootloader boot again ;)
vfs/{b|btr|package|b}fs/ext2/exfat: common access check.

* Added VFS helper function check_access_permissions() that combines
  several partially correct versions to the one true version (tm).
* All but BFS (since recently) missed the S_IXOTH for root on directories,
  and all but packagefs missed proper group handling.
fs_shell: Added missing new permission check function.

* Fixes the build.