[ARM] Orion: provide GPIO method for enabling hardware assisted blinking

This is a pre-requisite for implementing proper hardware accelerated
GPIO LED flashing, and since we want proper locking, it's sensible to provide
the orion specific orion_gpio_set_blink() implementation within
mach-orion/gpio.c. The functions orion_gpio_set_blink() and gpio_set_value()
implicitly turn off each others state.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Acked-by: Tzachi Perelstein <tzachi@marvell.com>
Acked-by: Nicolas Pitre <nico@marvell.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>