servo: Cleanup EC3PO interfaces

There were some hard-code rules to detect the case for USB PD on servo
v2. As servo v2 doesn't have a dedicated UART for USB PD. It requires
repurposing JTAGS pins for USB PD UART instead. Only the boards with
USBPD define the 'usbpd_uart_pty'.

This change removes the rules and defines the corresponding raw uart
in the servo_interfaces. If no control defines the raw uart (the case
of USB PD), it simply doesn't initialize the interface, as it is
expected that no one will use the raw uart and its EC3PO uart.

BUG=b:37473185
TEST=On servo v2, started servod on Reef, verified EC3PO UART for EC,
and no EC3PO UART for USB PD.

Change-Id: If1ed227ca92fa2245605551e62db1a649bc04b35
Reviewed-on: https://chromium-review.googlesource.com/489321
Commit-Ready: Wai-Hong Tam <waihong@google.com>
Tested-by: Wai-Hong Tam <waihong@google.com>
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
2 files changed