Revert "MIPS: Delete unused function add_temporary_entry."

This reverts commit d7a887a7.

Function add_temporary_entry is needed by bcm47xx to support highmem. We
need to add a temporary entry to check for amount of RAM.
The only change made in this revert was replacing (ENTER|EXIT)_CRITICAL.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: https://patchwork.linux-mips.org/patch/7395/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>