msm: acpuclock-krait: Detect and preserve CPU and L2 clock rates at boot

Previously, the acpuclock-krait driver changed the rates of these clocks
at boot to match the highest performance levels in acpu_freq_tbl. Instead,
detect and preserve the bootloader configuration until acpuclk_set_rate()
is called. This gets acpuclock-krait out of the business of deciding what
rates the CPUs should be running at, and leaves such policy decisions to
the drivers which call it.

Change-Id: I4feba569c471ca3b08cb5201ab65436503b4455e
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>