target/cortex_m: allow setting the type of a breakpoint

target/cortex_m: allow setting the type of a breakpoint

Cortex-M target used 'auto_bp_type' mode. The requested type
of breakpoint was ignored and hard (FPB) breakpoints were set in
'code memory area' 0x00000000-0x1fffffff, soft breakpoints were set above
0x20000000.

The code memory area of Cortex-M does not mean the memory is flash and
vice versa. External flash (parallel or QSPI) is usually mapped above
code memory area. Cortex-M7 ITCM RAM is mapped at 0. Kinetis
has a RAM block under 0x20000000 boundary.

Remove 'auto_bp_type' mode, set breakpoints to requested type.

Change 'cortex_m maskisr auto' handling to use a hard temporary
breakpoint everywhere: it can also workaround not working soft breakpoints
on Cortex-M7 with ICache enabled.

Change-Id: I7a9f9464c5e10bfd7f17cba1037ed07a064fa2e8
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4429
Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>