drm/lima: Add optional devfreq and cooling device support

Most platforms with a Mali-400 or Mali-450 GPU also have support for
changing the GPU clock frequency. Add devfreq support so the GPU clock
rate is updated based on the actual GPU usage when the
"operating-points-v2" property is present in the board.dts.

The actual devfreq code is taken from panfrost_devfreq.c and modified so
it matches what the lima hardware needs:
- a call to dev_pm_opp_set_clkname() during initialization because there
  are two clocks on Mali-4x0 IPs. "core" is the one that actually clocks
  the GPU so we need to control it using devfreq.
- locking when reading or writing the devfreq statistics because (unlike
  than panfrost) we have multiple PP and GP IRQs which may finish jobs
  concurrently.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200319203427.2259891-3-martin.blumenstingl@googlemail.com