pckbd: alter i8042_mm_init() to return a I8042_MMIO device

This exposes the I8042_MMIO device to the caller to allow the register memory
region to be mapped outside of i8042_mm_init().

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Helge Deller <deller@gmx.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20220624134109.881989-28-mark.cave-ayland@ilande.co.uk>
2 files changed