lpcspifi: setup a valid stack pointer before calling ROM code using stack

lpcspifi: setup a valid stack pointer before calling ROM code using stack

The spifi_init_code blob is calling the spifi_init() function from the ROM.
This ROM function is making use of the stack. So if the stack pointer is
invalid, trying to execute this code leads to a double fault and the
target_run_algorithm() call return with an error.
This patch simply ensure that the stack pointer is properly setup before
calling the spifi_init() ROM function.

Change-Id: I42a2163cfc2c6dfe5ada97ae8eb2bb6d2e283ff7
Signed-off-by: Aurelien Jacobs <aurel@gnuage.org>
Reviewed-on: http://openocd.zylin.com/1836
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>