Cortex-M: Detect Flash Patch Revision and implement Rev. 2 handling.

E.g. STM32F7 implements Rev.2.
Supercedes abandoned patch 2755 that doesn't evaluate Flash patch revision.

Change-Id: I48756b0451c7359475066969c900978a536bc328
Signed-off-by: Uwe Bonnes <bon@elektron.ikp.physik.tu-darmstadt.de>
Reviewed-on: http://openocd.zylin.com/2868
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/target/cortex_m.h

@@ -175,6 +175,7 @@ struct cortex_m_common {
 	int fp_num_lit;
 	int fp_num_code;
 	int fp_code_available;
+	int fp_rev;
 	int fpb_enabled;
 	int auto_bp_type;
 	struct cortex_m_fp_comparator *fp_comparator_list;