() Rename nsim_uart.c to uart_nsim.c. This is to follow
the driver naming convention.
() Rename functions nsim_uart_*() to uart_nsim_*(),
following driver naming convention.
() UART ports initialization is moved into the driver itself.
All the init code in platform config files is removed.
() Adds (many) Kconfig options. These don't have to be defined
in each platform's board.h anymore.
Change-Id: If015f39a6f6b4fcc65625e6e5f973b4469202f54
Signed-off-by: Daniel Leung <daniel.leung@intel.com>