ARM: dts: bcm283x: Restore simple-bus to /clocks

Commit [1] ([2] upstream) removed the "simple-bus" compatible string,
"#address-cells" and "#size-cells" to fix some DT scheme warnings. In
doing so it prevented the child clocks from being instantiated - the
node might as well be absent.

Fix the problem (at least with regards to functionality) by restoring
"simple-bus" and the sizes.

See: https://github.com/raspberrypi/linux/issues/3481


Fixes: [1] 238506eb ("ARM: dts: bcm283x: Remove simple-bus from fixed clocks")
Fixes: [2] 4b2d2466 ("ARM: dts: bcm283x: Remove simple-bus from fixed clocks")

Signed-off-by: Phil Elwell <phil@raspberrypi.com>