cpu_boost: Only restore minfreq to CPU0

Previously, when a non-primary CPU core was boosted, if it was offline after a boost expired, then the minfreq on that CPU would still be set to the boost frequency. Minfreq is now synced across all cores in msm/cpufreq, so we only need to restore the minfreq to CPU0.

Signed-off-by: Sultanxda <sultanxda@gmail.com>
cpu_boost: Clean up minfreq restoration

Signed-off-by: Sultanxda <sultanxda@gmail.com>

Conflicts:
	drivers/cpufreq/cpu_boost.c
retain_cpu_freq: Rename to retain_cpu_policy
cpu_boost: derp
retain_cpu_policy: Improve logic for checks
cpu_boost: Apply retain_cpu_policy logic to boosts

Policies will fall back to cpu0 if unavailable.
retain_cpu_policy: Add a fail-safe

Deliberately NULLify variables if things are failing, so that the checks will catch it.
cpufreq: Add conditions for when retain_cpu_policy is disabled