usb: pd: qpnp-pdphy: Fix reception of Get_Battery_Cap

Get_Battery_Cap is a PD 3.0 extended message but has the same
MessageID as a BIST data message. Currently the handling for
the latter mistakenly treats Get_Battery_Cap as a BIST and
does not pass it up to the policy engine. Fix this by adding
a check for the 15th bit of the message header which indicates
it is an extended message.

Change-Id: I5ebe4dc3c765303a570b48e47dfb2e40750b3843
Signed-off-by: Jack Pham <jackp@codeaurora.org>