da850: add new config file for AM18xx

add new configuration file da850_am18xxevm.h for AM18xx boards
which are based on da850 SOC. AM18xx has WINBOND spi flash which
is indicated in the config file. And make appropriate changes in
board.cfg for building.

Signed-off-by: Nagabhushana Netagunte <nagabhushana.netagunte@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
diff --git a/boards.cfg b/boards.cfg
index 7113745..cf6e67c 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -121,6 +121,7 @@
 pm9g45                       arm         arm926ejs   pm9g45              ronetix        at91        pm9g45:AT91SAM9G45
 da830evm                     arm         arm926ejs   da8xxevm            davinci        davinci
 da850evm                     arm         arm926ejs   da8xxevm            davinci        davinci
+da850_am18xxevm              arm         arm926ejs   da8xxevm            davinci        davinci
 cam_enc_4xx                  arm         arm926ejs   cam_enc_4xx         ait            davinci     cam_enc_4xx
 hawkboard                    arm         arm926ejs   da8xxevm            davinci        davinci
 hawkboard_nand               arm         arm926ejs   da8xxevm            davinci        davinci     hawkboard:NAND_U_BOOT