dts: mpc512x: add clock specs for client lookups

this addresses the client side of device tree based clock lookups

add clock specifiers to the mbx, nfc, mscan, sdhc, i2c, axe, diu, viu,
mdio, fec, usb, pata, psc, psc fifo, and pci nodes in the shared
mpc5121.dtsi include

Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: devicetree@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Reviewed-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>