mhi: cntrl: bus scale adjustments based on requested GEN speeds

Modify bus scale frequency requests based on device requested
GEN speeds for PCIe link.

CRs-Fixed: 2479785
Change-Id: Id6ee5d03b1bb9b293a954122eaa05b75557bf977
Acked-by: Bhaumik Vasav Bhatt <bbhatt@qti.qualcomm.com>
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>