msm: buspm: Enable busPM for targets which support bus scaling.

BusPM module should not depend on individual target configs
as it previously was. Fix this by tying busPM module with
MSM_BUS_SCALING conifg and enable it on all targets where
bus scaling is enabled.

CRs-Fixed: 486454
Change-Id: I5e44b6b63dd8577a5db6fa6f34526af0a4933c82
Signed-off-by: Gagan Mac <gmac@codeaurora.org>