[POWERPC] Fix RTC and device tree on linkstation machines

This fixes the RTC on linkstation ppc machines again, and updates the
device tree: add rtc nodes on i2c, remove bogus 0-size cache-line
declarations, rename interrupt-controller nodes, remove erroneous
interrupt-parent line, accidentally introduced by a recent patch.

Signed-off-by: G. Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>