mhi: core: device requested bandwidth scaling support

Device can request scaling for the PCIe link speeds and width
through MHI. Added support for handling the same.

CRs-Fixed: 2479785
Change-Id: Ia22f2d048c862e5c5aa057503b8072cf4cebf835
Acked-by: Bhaumik Vasav Bhatt <bbhatt@qti.qualcomm.com>
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>