ARM: shmobile: marzen-reference: Instantiate clkdevs for SCIF and TMU

Now that the common clock framework is supported, the clock lookup
entries in clock-r8a7779.c are not registered anymore. Devices must
instead reference their clocks in the device tree. However, SCIF and CMT
devices are still instantiated through platform code, and thus need a
clock lookup entry.

Retrieve the SCIF and CMT clock entries by name and register clkdevs for
the corresponding devices. This will be removed when the SCIF and CMT
devices will be instantiated from the device tree.

Based on work for the Koelsch board by Laurent Pinchart.

Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>