fbdev: Align deferred I/O with naming of helpers

Deferred-I/O generator macros generate callbacks for struct fb_ops
that operate on memory ranges in I/O address space or system address
space. Rename the macros to use the _IOMEM_ and _SYSMEM_ infixes of
their underlying helpers. Adapt all users. No functional changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230729193157.15446-5-tzimmermann@suse.de