msm: mhi_dev: Allocate ring element during M0

Device allocates ring memory during mmio initialization, this
causes 128 event ring elements to be created as MHICFG
register may not be updated by the host. This causes memory
to get exhausted leading to an MMIO init failure.

The Change is to allocate ring memory during M0, during which
MHICFG register is bound to be updated by the host.

Change-Id: I04a0e0ed79a46f16f96e2be4c5c68cba9ee2c99d
Signed-off-by: Subramanian Ananthanarayanan <skananth@codeaurora.org>
Signed-off-by: Gauri Joshi <gaurjosh@codeaurora.org>