mhi: core: Enable correct channel alignment

Enable correct allignment of MHI channels to the
ring size rounded up to the next power of two as
per device requirement.

Change-Id: Ic77c43fdbcde2ec3b6f08e3062eaf778eb13ec5b
Signed-off-by: Andrei Danaila <adanaila@codeaurora.org>
Signed-off-by: Tony Truong <truong@codeaurora.org>