soc: qcom: smd: Represent channel layout in structures

The rx and tx channel info are laid out in memory next to each
other, and there are two types of channel info structures, byte
based and word based. We have 4 pointers to these info
structures, when we really only need two to point to the
different types of structures. Encapsulate the byte based and
word based tx/rx structures in a "channel pair" structure that
describes the layout of memory and reduces the number of pointers
in the smd channel structure by two.

Reviewed-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Andy Gross <agross@codeaurora.org>