[ARM] 4805/1: ixp4xx: Use leds-gpio driver instead of IXP4XX-GPIO-LED driver

These are the only three boards to use the IXP4XX-GPIO-LED driver, and
they can all use the new leds-gpio driver instead with no change in
functionality.

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Signed-off-by: Rod Whitby <rod@whitby.id.au>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>