misc: add gpio based status led driver

This patch adds a status led driver followed the GPIO access
conventions of Linux. The led mask is used to specify the gpio pin.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Tested-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>