[PATCH] powerpc: Add support for Book-E timer config to generic_calibrate_decr

We need to initialize some control SPRS for timers on Book-E before
we start taking decrementer interrupts.

Signed-off-by: Kumar K. Gala <kumar.gala@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>