mali_kbase: platform: Set Pixel integration log level from DT

Currently the Pixel integration of the Mali GPU KMD hardcodes the
verbosity of its output. This is updated to enable configuring log
level via device tree. This patch uses the GPU log level set from
the device tree to set initial verbosity level.

Bug: 163528916
Signed-off-by: Devika Krishnadas <kdevika@google.com>
Change-Id: I156ad6d59a3510258580849ed4004e60ff0ebfd8