drm/lima: recover task by enlarging heap buffer

Increase heap buffer backup memory when GP receive PLBU
out of memory interrupt, then resume the task.

Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Tested-by: Andreas Baierl <ichgeh@imkreisrum.de>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200116131157.13346-5-yuq825@gmail.com