mt6765-common: perf: Allow raising sched_boost to 6 levels

Kernel supports boosting upto 6 different levels of sched boost.
Limiting it to only two seems like a waste of useful resources that
we already have in hand.

Signed-off-by: Vaisakh Murali <mvaisakh@statixos.com>
Change-Id: Ia1f6b698e6c853e260743509448ba55a7afef816