fbdev: Rename fb_mem*() helpers

Update the names of the fb_mem*() helpers to be consistent with their
regular counterparts. Hence, fb_memset() now becomes fb_memset_io(),
fb_memcpy_fromfb() now becomes fb_memcpy_fromio() and fb_memcpy_tofb()
becomes fb_memcpy_toio(). No functional changes.

v6:
	* update new file fb_io_fops.c

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20230512102444.5438-8-tzimmermann@suse.de