ARM: dts: msm: Set start and end MHI event ring ids for sdxpoorwills

MHI event ring ids used by IPA GSI channels
need to be chosen from a pre-defined range.
Here we define the range limits (start and end numbers).
Making the range limits configurable by dts will make it
easier to tune them between different targets.

Change-Id: I17f4cbfa1534cf4b1d4e8366f6e027fadc3df75f
CRs-fixed: 2134421
Signed-off-by: Ghanim Fodi <gfodi@codeaurora.org>