rpi: add uart device_path

Currently there is no device_path registered for UART in Raspberry Pi
source. This will hinder the working of UART driver in mraa.

So, register the device_path with '/dev/serial0' as most of the
raspbian images make this as a soft link to _real_ UART port by
default.

Tested-on: Raspberry pi 3 model B

Signed-off-by: Manivannan Sadhasivam <[email protected]>

Author: Mani-Sadhasivam

src/arm/raspberry_pi.c

@@ -834,6 +834,7 @@ mraa_raspberry_pi()
     b->def_uart_dev = 0;
     b->uart_dev[0].rx = 10;
     b->uart_dev[0].tx = 8;
+    b->uart_dev[0].device_path = "/dev/serial0";
 
     if ((platform_detected == PLATFORM_RASPBERRY_PI_A_PLUS_REV_1) ||
         (platform_detected == PLATFORM_RASPBERRY_PI_B_PLUS_REV_1) ||