msm: devices msm7627a: *GPU overclock*

this prepares the ability to overclock the GPU

   NOTE: the gpu driver currently uses to set the GPU's clock
         to the highest possible value!

   Valid frequency ranges for Adreno203 are:
         245 Mhz <-> 400 Mhz

   Recommended Value: --- 320 Mhz ---

!!!   OVERCLOCKING IS ALWAYS INVOKING THE RISK OF DESTRUCTION   !!!
              !!!   DO IT ON YOUR RISK   !!!
drivers/cpufreq: conservative: simplified SAMPLING_TIME determination

...because simple things can be good things, too.

This commit introduces MIN_SAMPLING_RATE & DEF_SAMPLING_RATE
which are used to directly set the driver's minimum and default
sampling rate rather than doing any calculation before.

DEF_FREQUENCY_DOWN_THRESHOLD gets increased to a more reasonable value.
Makefile: allow GCC flag overriding