LaCie/common: add support for the CPLD GPIO bus

LaCie/common: add support for the CPLD GPIO bus

This patch adds support for the CPLD GPIO bus found on some LaCie boards
(as the 2Big/5Big Network v2 and the 2Big NAS). This parallel GPIO bus
exposes two registers (address and data). Each of this register is made
up of several dedicated GPIOs. An extra GPIO is used to notify the CPLD
that the registers have been updated.

Mostly this bus is used to configure the LEDs on LaCie boards.

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>