blackfin: Move blackfin serial driver out of blackfin arch folder.

- Move blackfin serial driver to the generic driver folder.
- Move blackfin serial headers to blackfin arch head folder.
- Update the include path to blackfin serial header in start up code.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>

include/configs/bfin_adi_common.h

@@ -111,6 +111,9 @@
 #ifndef CONFIG_BAUDRATE
 # define CONFIG_BAUDRATE	57600
 #endif
+#ifdef CONFIG_UART_CONSOLE
+# define CONFIG_BFIN_SERIAL
+#endif
 
 /*
  * Debug Settings