mfd: vexpress-sysreg: Remove LEDs code

As the current LEDs code breaks other platform, remove it.

It shall be replaced by a generic "MMIO LEDs" driver.

Reported-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>