Adapt CLI to use new libflashrom interface' print callback

This renames CLI's print() to flashrom_print_cb() and registers it
through the new libflashrom interface.

v2: Add libflashrom.o to LIB_OBJS now that everything can be linked
    together.

Change-Id: Idf19978eb8e340d258199193d2978f37409e9983
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/17948
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>

flash.h

@@ -30,6 +30,7 @@
 #include <stdio.h>
 #include <stdint.h>
 #include <stddef.h>
+#include <stdarg.h>
 #include <stdbool.h>
 #if IS_WINDOWS
 #include <windows.h>
@@ -321,6 +322,7 @@ enum msglevel {
 	MSG_DEBUG2	= 4,
 	MSG_SPEW	= 5,
 };
+int flashrom_print_cb(enum msglevel level, const char *fmt, va_list ap);
 /* Let gcc and clang check for correct printf-style format strings. */
 int print(enum msglevel level, const char *fmt, ...)
 #ifdef __MINGW32__