msm: acpuclock-cortex: Detect bootloader cpu configuration

Detect which cpu rate is currently selected by the bootloaders during
probe. If the rate is invalid, then set the cpu rate to maximum.

Change-Id: I316d5de76133e76993a47b0d2917fd35bc5dd590
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>