usb: dwc3-msm: dbm: Generalize register offset calculations

The DBM submodule of the DWC3 MSM USB controller block has had
different register maps depending on the SoC. Currently the
device tree bindings use different compatible ids to make this
distinction, and will map to either the '1.4' or '1.5' version
of the driver.

But since there aren't major differences between the two versions
other than the register offsets, it makes sense to try to converge
into a single driver. To that end, deal with the offsets by
looking them up in a table based on version instead of using
hardcoded #defines. This patch does just that for '1.5' for now.

Change-Id: Ibbf2b8a69d7568f3ddb7b5810ecfcacd9ce5a7fe
Signed-off-by: Jack Pham <jackp@codeaurora.org>