cfi: Make the flash erase and write operations abortable

Check for ctrlc() in operations that take time and loop over the flash
addresses.

In netconsole, tstc() is expensive.  Only check once in a while to not
slow down the operation significantly.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/include/flash.h b/include/flash.h
index e614d07..6d70bdd 100644
--- a/include/flash.h
+++ b/include/flash.h
@@ -141,6 +141,7 @@
 #define ERR_UNKNOWN_FLASH_VENDOR	32
 #define ERR_UNKNOWN_FLASH_TYPE		64
 #define ERR_PROG_ERROR			128
+#define ERR_ABORTED			256
 
 /*-----------------------------------------------------------------------
  * Protection Flags for flash_protect():