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 using a app like Trickster MOD

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

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

	-Fix warning "drivers/cpufreq/cpufreq.c:721:14: warning: unused variable 'host1x'
	 [-Wunused-variable] struct clk *host1x = tegra_get_clock_by_name("host1x");"

	-Fix 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");"

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