user_channel: Get Channel Payload Support command refactor

Update the get channel payload support command to use the new IPMI API.
This simplifies the code as well as adds support for the special IPMI
channel 0x0e.

Tested: ipmitool -I lanplus -H ... -U ... raw 6 0x4e 0xe
         03 00 3f 00 00 00 00 00
        ipmitool -I lanplus -H ... -U ... raw 6 0x4e 1
         03 00 3f 00 00 00 00 00

Change-Id: I8b67d6f79c40299b4b653212a2f1f9d0c1a9087c
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
2 files changed