drm/amdgpu: Vega20 SMU I2C HW engine controller.

drm/amdgpu: Vega20 SMU I2C HW engine controller.

Implement HW I2C enigne controller to be used by the RAS EEPROM
table manager. This is based on code from ATITOOLs.

v2:
Rename the file and all function prefixes to smu_v11_0_i2c

By Luben's observation always fill the TX fifo to full so
we don't have garbadge interpreted by the slave as valid data.

v3:
Remove preemption disable as the HW I2C controller will not
stop the clock on empty TX fifo and so it's not critical to
keep not empty queue.
Switch to fast mode 400 khz SCL clock for faster read and write.

v5:
Restore clock gating before releasing I2C bus and fix some
style comments.

v6:
squash in warning fix, fix includes (Alex)

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Luben Tuikov <Luben.Tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>