mhi: core: expose current state of MHI device to clients

Some MHI control drivers and MHI clients needs current MHI device
state, and execution environment to handle client specific
requirements.

CRs-Fixed: 2287705
Change-Id: I363508b393cc1e63827158b8b9f094ab380cb97c
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>