staging: sm7xx: Use kernel framebuffer mode setting

This patch implements dynamic framebuffer mode setting.

Previous code works with mode setting in a hard code way. Previous hard
code configuration is used as default configuration if dynamic mode
setting or boot mode setting (via sm712vga_setup) is not used.

Tested with SM712 supporting 1024x600x16 as default hardware resolution.

Changes:

- Implement fb_check_var and fb_set_par callbacks
- Remove __maybe_unused decorator in function being used (sm712vga_setup)
- Minor cleanup on initialization structs related with mode settings
- Updated author copyright
- Updated TODO file

Signed-off-by: Javier M. Mellid <jmunhoz@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>