PM / devfreq: memlat: Add support for compute-bound logic

Currently, an entirely separate governor is used to handle compute-bound
cases.  Roll this functionality into the existing memlat governor and
allow devices to choose which logic to target by specifying different
drivers in the 'compatible' field.

Change-Id: I8dc41bf0474309c3564dec8e6c813511b8a7fc02
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>