synquacer: Add a make option to select UART port

This patch adds a new make option to select UART port
in make and CMake build on SynQuacer platform.

The following 3 UART ports are selectable.
uart0 : A standard UART on the 40 pin expansion connector
        (used as default for SCP console)
uart1 : A second standard UART on the 40 pin expansion connector
debug_uart : A debug UART via the micro-B USB connector

To select UART port, set SYNQUACER_UART value as below
when executing make commnad.

In make build system,
make CC=$CC PRODUCT=synquacer MODE=$MODE \
 [SYNQUACER_UART=uart0|uart1|debug_uart]
e.g.
make CC=$CC PRODUCT=synquacer MODE=$MODE SYNQUACER_UART=uart1

In CMake build system,
make -f Makefile.cmake CC=$CC PRODUCT=synquacer MODE=$MODE \
 [EXTRA_CONFIG_ARGS="-DSYNQUACER_UART=uart0|uart1|debug_uart"]
e.g.
make -f Makefile.cmake CC=$CC PRODUCT=synquacer MODE=$MODE \
 EXTRA_CONFIG_ARGS="-DSYNQUACER_UART=uart1"

If SYNQUACER_UART value is not set, uart0 is selected as defalut.

Change-Id: I9390a178c4685d5e4aa88d1eb1174aa9a26fd00f
Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Signed-off-by: Masanobu Morikawa <morikawa.masanobu@socionext.com>