leds: provide helper to register "leds-gpio" devices

This function makes a deep copy of the platform data to allow it to live
in init memory.  For a kernel that supports several machines and so
includes the definition for several leds-gpio devices this saves quite
some memory because all but one definition can be free'd after boot.

As the function is used by arch code it must be builtin and so cannot go
into leds-gpio.c.

[akpm@linux-foundation.org: s/CONFIG_LED_REGISTER_GPIO/CONFIG_LEDS_REGISTER_GPIO/]
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Russell King <rmk@arm.linux.org.uk>
Acked-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: H Hartley Sweeten <hartleys@visionengravers.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>