RTOS support: Add FPU support for FreeRTOS

RTOS support: Add FPU support for FreeRTOS

Add new structure for for working with FPU thread in thread view.
This modification support both stacking.
When FPU is activated, LR must be validated to check if the FPU
register are push on the stack. This is mandatory to find the correct
stack pointer position.

the modified code was inspired and adapted from

https://github.com/TauLabs/TauLabs/commit/88d2003bb83a6b72c796274c889e307f96645966

Change-Id: I6641926aa14e7216cacb399cbc8bb0db324cc9fc
Signed-off-by: Jonathan Dumaresq <jdumaresq@cimeq.qc.ca>
Reviewed-on: http://openocd.zylin.com/3397
Tested-by: jenkins
Reviewed-by: Sergey A. Borshch <sb-sf@users.sourceforge.net>
Reviewed-by: Harry Zhurov <harry.zhurov@gmail.com>
Reviewed-by: Anton Gusev
Reviewed-by: Михаил Цивинский <mtsivinsky@gmail.com>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>