MIPS: SEAD3: Use register-bit-led driver via DT for LEDs

Probe a driver for the PLED & FLED LEDs found on the SEAD3 board using
the register-bit-led driver via device tree, rather than a custom driver
via platform code. Enable support for the register-bit-led driver & its
prerequisite syscon in sead3_defconfig.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Jacek Anaszewski <j.anaszewski@samsung.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14054/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>