rtos: Fix XPSR_OFFSET for cortex_m4f stacking

rtos: Fix XPSR_OFFSET for cortex_m4f stacking

Structures rtos_standard_Cortex_M4F_stacking and
rtos_standard_Cortex_M4F_FPU_stacking in rtos_standard_stackings.c
where using rtos_standard_Cortex_M3_stack_align for the stack-align
function. This function calls rtos_Cortex_M_stack_align with
XPSR_OFFSET = 0x3c. This offset is correct for cortex-M3 but not for
cortex-M4F and cortex-M4F with fpu. This patch adds stack_align
functions for M4F an M4F_FPU

Change-Id: If6a90b1898fccbb85619a10f3aef5277dd88ce47
Signed-off-by: Armin van der Togt <armin@otheruse.nl>
Reviewed-on: http://openocd.zylin.com/4037
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>