target-xtensa: esp8266: pass UART name to init function

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: esp8266: add pinmux

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target-xtensa: esp8266: add SPI interface

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>