stm32: update stm32f1x driver for f0x and f3x option bytes

The stm32f0 and stm32f3 share the same option byte location, but the format
differs.

Adding an option_offset fixes the broken options_read cmd and incorrectly
setting Hardware Watchdog when unlocking a f3x device.

Change-Id: I82d66b6198294ea9eedb44ca8b2fb368c0cb15e8
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1184
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>
flash: fix stm32 failed probe using incorrect flash size

This fixes an issue if the device is manually probed after the initial probe
fails due to being unable to read flash size register. In this situation the
driver assumes the user has overridden the flash size when infact this may
not be the case.

It also seems on the older stm32f1 devices the flash register is not readable
when locked, this does not seem to apply to the newer parts - f0, f3, f4.

Change-Id: I125f872fcb2d962ca6705f97b62d957e2b31303b
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1187
Tested-by: jenkins
Reviewed-by: Johan Almquist <johan.almquist@assaabloy.com>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>