flash Kinetis: add KL8x family, fix erase check

Secure devices KL81Z7 and KL82Z7 have no SERIESID field in ID register
so they have to be decoded in Kx branch (not KLx).

The flash controller in KL8x and also in K8x devices does not implement
FTFx_CMD_BLOCKSTAT command. Fix kinetis_blank_check() to work properly
using FTFx_CMD_SECTSTAT command only.
Introduce a new flag FS_NO_CMD_BLOCKSTAT to avoid use of FTFx_CMD_BLOCKSTAT
on these devices.

Change-Id: I3ff58718480acd8cce69f618f71667b6b1d9c4f3
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3898


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