cpufreq: Add Loongson machine dependencies

The MIPS loongson cpufreq drivers don't build unless configured for the
correct machine type, due to dependency on machine specific architecture
headers and symbols in machine specific platform code.

More specifically loongson1-cpufreq.c uses RST_CPU_EN and RST_CPU,
neither of which is defined in asm/mach-loongson32/regs-clk.h unless
CONFIG_LOONGSON1_LS1B=y, and loongson2_cpufreq.c references
loongson2_clockmod_table[], which is only defined in
arch/mips/loongson64/lemote-2f/clock.c, i.e. when
CONFIG_LEMOTE_MACH2F=y.

Add these dependencies to Kconfig to avoid randconfig / allyesconfig
build failures (e.g. when based on BMIPS which also has a cpufreq
driver).

Signed-off-by: James Hogan <jhogan@kernel.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>