mhi: core: exit low power mode before calling client probe

MHI clients require external modem to be in active state when
clients probe is getting called because they may access physical
link directly. To avoid un-clock register access, exit low power
before calling clients probe function.

CRs-Fixed: 2329469
Change-Id: Ib48f003b6e2e53c1cc026219fe3edab6253deec4
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>