ARM: shmobile: armadillo: Add PWM backlight power supply

Commit 22ceeee1 ("pwm-backlight: Add
power supply support") added a mandatory power supply for the PWM
backlight. Add a fixed 5V regulator to board code with a consumer supply
entry for the backlight device.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
(cherry picked from commit ad11cb9a5cf96346f1240995c672cdbb5501785c)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>