kinetis : improve kinetis flash driver.

kinetis : improve kinetis flash driver.

Kinetis K-series have different guranuarity for each frequency model.
This patch adding more minute guranuarity detection.
And adopted mass erase command not only L-series but also K-series.
Tested on MK20DX32VLF5,MK10DX32VLF5,and MKL25Z128VLK4.

Change-Id: Iffef850d4b388463756a13faf02c3890bfc19acf
Signed-off-by: Nemui Trinomius <nemuisan_kawausogasuki@live.jp>
Reviewed-on: http://openocd.zylin.com/1894
Tested-by: jenkins
Reviewed-by: Per Ekman <pekenator@gmail.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-by: Mateusz Kaduk <mateusz.kaduk@gmail.com>