Revert "drm/ttm: never consider pinned BOs for eviction&swap"

This reverts commit 8996b130 which is
commit a2848d08 upstream.

It breaks the Android kernel abi, and is not needed for any Android
devices at this time.  If it is needed in the future, it can be brought
back in an abi-safe way.

Bug: 161946584
Change-Id: I9d6e3021fdefbab998d058e1b4ab8d559f26aec3
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>