drm/radeon: Fix coding style in fbdev emulation

Fix the coding style in several places in the fbdev-emulation
code. Also rename functions and structure file by comments. No
functional changes.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>