HID: rmi: Protect PM-only functions by #ifdef CONFIG_PM

If CONFIG_PM=n:

drivers/hid/hid-rmi.c:432: warning: ‘rmi_post_reset’ defined but not used
drivers/hid/hid-rmi.c:437: warning: ‘rmi_post_resume’ defined but not used

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>