USB: HID: Steelseries SRW-S1 Add support controlling all LEDs simultaneously

This patch to the SRW-S1 driver adds the ability to control all
LEDs simultaneously as testing showed that it was slow (noticably!!)
when seting or clearing all the LEDs in turn.

It adds a 'RPMALL' LED, whose behavoir is asserted to all the LEDs in
the bar graph, individual LEDs can subsequently be turned on/off
individually.

Signed-off-by: Simon Wood <simon@mungewell.org>
Tested-by: John Murphy <rosegardener@freeode.co.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>