HID: input: add mapping for keyboard Brightness Up/Down/Toggle keys

[ Upstream commit 7975a1d6a7afeb3eb61c971a153d24dd8fa032f3 ]

According to HUTRR73 usages 0x79, 0x7a and 0x7c from the consumer page
correspond to Brightness Up/Down/Toggle keys, so let's add the mappings.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>