flash Kinetis: refactoring ftfx commands and numerous minor changes

flash Kinetis: refactoring ftfx commands and numerous minor changes

Add kinetis_ftfx_decode_error() to show flash error type in human
readable message.

Add kinetis_ftfx_prepare() to prepare flash module just once in
command (not each time kinetis_ftfx_command() is called).

Change target_read/write_memory() to target_read/write_u8/32().

Make ftfx_fstat parameter of kinetis_ftfx_command() optional.

Longword flash write:
Fix huge memory leak after write of unaligned block.
Check flash address alignment properly.
Do not fill whole padding buffer but its end after original data.
Remove duplicite padding.

Change-Id: Ia5e312909f68d3cc724c8cbffe1cd903b9102124
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3561
Tested-by: jenkins
Reviewed-by: Steven Stallion <stallion@squareup.com>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>