MLK-16075-1 gpu: imx: dpu: fetchdecode: Update funcs to enable/disable src buf
The bit to enable/disable source buffer is embedded in the register
LAYERPORPERTY0. However, the other bits of the register may have
other functionalities. So, using fetchdecode_layerproperty() to
enable/disable source buffer isn't appropriate. This patch uses
new functions to enable/disable fetchdecode source buffer so that
the function names could be a bit specific about what they are doing.
Signed-off-by: Liu Ying <victor.liu@nxp.com>