drm: fb: Modify check to ensure correctness of flags

drm: fb: Modify check to ensure correctness of flags

This patch also modifies the validation of framebuffer flags in DRM
core framework. This is to ensure that application is setting the
right framebuffer flags.

Signed-off-by: Satish Kumar Nagireddy <satish.nagireddy.nagireddy@xilinx.com>
Reviewed-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>