topic: Added support for the SAM4S variants

topic: Added support for the SAM4S variants

Atmel introduced 6 new Cortex-M4 processors on 2011-10-26
SAM4S16C - 1024KB flash LQFP100/BGA100
SAM4S16B - 1024KB flash LQFP64/QFN64
SAM4S16A - 1024KB flash LQFP48/QFN48
SAM4S8C - 512KB flash LQFP100/BGA100
SAM4S8B - 512KB flash LQFP64/QFN64
SAM4S8A - 512KB flash LQFP48/QFN48

The SAM4S processors still suffer from the "6 waitstates needed
to program device" errata.

Other relevant changes are:
1. Address of flash memory starts at 0x400000.
2. EWP (Erase page and write page) only works for the first two 8KB "sectors"
3. Because of the EWP not working for all the sectors, normal page writes have
to be used.  The default_flash_blank_check is used to check if lockregions
should be erased.
4. The EA (Erase All) command takes 7.3s to complete. (Previous timeout was
500 ms)
5. There are 128 lockable regions of 8KB each.

Implemented default blank checking, and page erase for load_image scenarios.
This is to compensate for the EWP flash commands only working on the
first 2 8KB sectors.

Change-Id: I7c5a52b177f7849a107611fd0f635fc416cfb724
Signed-off-by: Olivier Schonken <olivier.schonken@gmail.com>
Reviewed-on: http://openocd.zylin.com/528
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>