fbdev: Add initializer macros for struct fb_ops

For framebuffers in I/O and system memory, add macros that set
struct fb_ops to the respective callback functions.

For deferred I/O, add macros that generate callback functions with
damage handling. Add initializer macros that set struct fb_ops to
the generated callbacks.

These macros can remove a lot boilerplate code from fbdev drivers.
The drivers are supposed to use the macro that is required for its
framebuffer. Each macro is split into smaller helpers, so that
drivers with non-standard callbacks can pick and customize callbacks
as needed. There are individual helper macros for read/write, mmap
and drawing.

v5:
	* fix whitespace errors (Jingfeng)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230530151228.22979-3-tzimmermann@suse.de