ARM: dts: i.MX53: move common QSB nodes to new file

There are (atleast) two versions of the i.MX53 LOCO:
            - the MCIMX53-START board
            - the MCIMX53-START-R board
The MCIMX53-START-R has a mc34708 pmic and is otherwise the similar to the
MCIMX53-START. To prepare for the START-R, move all common nodes to a new
imx53-qsb-common.dtsi and remove everything but the board name and pmic from
the imx53-qsb.dts.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>