cpufreq: cpu-boost: Increase sync thread policy and priority

More or less all cpufreq related threads run in a high priority.

Also, CMs patch series was somehow out of sync and incomplete,
readd the unchanged policy update to source cpu bit. And readd
the check for a possible corner case in try_to_wake_up() that
was already missing before.

Change-Id: Ibcc45217ff4b9323178b077754c4bb7c468984db
[zwliew: only increase priority]
Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>