flash Kinetis: implement automatic bank creation based on device probe

Kinetis flash driver services huge number of MCU types. They have
one, two or four flash banks with option of FlexNVM. It would
require ~36 config files just for Kx series, more for KLx, KVx and KE1x.

The change implements alternative approach:
- configuration file creates just one pflash bank (common for all devices)
- when a device is probed, additional pflash or flexnvm banks are created
based on flash layout of the connected MCU
- created banks have names with optional numbering e.g. kx.pflash0 kx.pflash1
kx.flexnvm0 kx.flexnvm1
- the first bank gets renamed if numbering is used

Automatic bank creation is enabled by tcl command 'kinetis create_banks'.

Used solution has a drawback: other banks than pflash0 are not accessible
until pflash0 is probed. Fortunately gdb attach and standard programming
accesses banks in right sequence.

Change-Id: I5b9037cbefdb8a4176b7715fbcc3af4da4c1ab60
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3925


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