Port @motley-git GPU overclocking interface

https://github.com/motley-git/Kernel-Nexus7

-Add a option to set default to stock GPU clock speed

-Stock GPU clock speed is default.  Can be adjusted at runtime

*Fix Warnings found in original patch in drivers/cpufreq/cpufreq.c

    -Remove unused int variable "unsigned int new_volt = 0;"

    -Fix unused variable warning "drivers/cpufreq/cpufreq.c:721:14: warning: unused variable 'host1x' [-Wunused-variable]
     struct clk *host1x = tegra_get_clock_by_name("host1x");"
     by adding "host1x->max_rate = new_gpu_freq;" and "host1x->dvfs->freqs[i] = new_gpu_freq;"

    -Fix unused variable warning "drivers/cpufreq/cpufreq.c:722:14: warning: unused variable 'pll_c' [-Wunused-variable]
     struct clk *pll_c = tegra_get_clock_by_name("pll_c");"
     by adding "pll_c->max_rate = new_gpu_freq;" and "pll_c->dvfs->freqs[i] = new_gpu_freq;"

Signed-off-by: Paul Beeler <sparksco@gmail.com>