userspace: set default priv stack size to 1024
userspace: set default priv stack size to 1024

The original value of 256 was selected more or less randomly
and special cases keep proliferating. Until we have a formal
method of proving maximum syscall stack depth, set to 1024.

Signed-off-by: Andrew Boie <aab045b28152628be6af0e556050d0381fd0a34d@intel.com>

nashif/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,Vudentz/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,ldts/zephyr,finikorg/zephyr,nashif/zephyr,ldts/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr