flash Kinetis: handle all types of watchdog, disable in reset-init

Active watchdog forces reset during armv7m_checksum_memory()
in verify_image command if run just after reset init.

COP watchdog in KL series and WDOG32 in KE1 series
have longer timeout however they need to be disabled too.

The change extends 'kinetis disable_wdog' command to optionally
probe the chip and use appropriate algorithm to disable watchdog.

Setting of cache type is also split from flash_support flags.

Tcl command 'kinetis disable_wdog' is called in reset-init event.

Change-Id: I3191e230f38b679ed74f2a97fe323ef8fb3fe22e
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3901


Tested-by: jenkins
Reviewed-by: Joakim Nohlgård <joakim.nohlgard@eistec.se>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>