usb: pd: combine into PE_SEND_SOFT_RESET

There is no major difference between PE_SRC_SEND_SOFT_RESET
and PE_SNK_SEND_SOFT_RESET states so merge them into one
state.

Change-Id: I9147c4460dd9adf107900e63abd46cd7c99b89d4
Signed-off-by: Jack Pham <jackp@codeaurora.org>