mhi: core: add support for overriding MHI channel context CHTYPE field

CHTYPE can be used to describe additional channel specific
properties apart from default channel direction. Add support
to override the default chtype using devicetree property.

CRs-Fixed: 2361266
Change-Id: I588cc61b1bbcc10fc38bb28efe4fdcdbbe64e3ab
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>