soc: qcom: glink_smd_xprt: replace magic numbers with constants

The channel state commands and channel offsets were used literally
instead of being stored in an enum or macro.

Replace literal numbers with macros.

Change-Id: I8824dea5baf44e89d769494a4ef542cb393c243a
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>