vcsm: Revert to do page-table-walk-based cache manipulating on some ioctl calls

vcsm: Revert to do page-table-walk-based cache manipulating on some ioctl calls

On FLUSH, INVALID, CLEAN_INVALID ioctl calls, cache operations based on
page table walk were used in case that the buffer of the cache is not
pinned.  So reverted to do page-table-based cache manipulating.

Signed-off-by: Sugizaki Yukimasa <i.can.speak.c.and.basic@gmail.com>
(cherry picked from commit b5a40e4b66f25056c1c2f30ea9a7d2d131672b75
https://github.com/raspberrypi/linux raspi/rpi-4.15.y)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>