tests: syscall: fix low value of CONFIG_MAX_THREAD_BYTES
tests: syscall: fix low value of CONFIG_MAX_THREAD_BYTES

Failed to build tests/kernel/mem_protect/syscalls on fvp_baser_aemv8r_smp
because the default value of CONFIG_MAX_THREAD_BYTES is too low.
So manually set the value to 5 in test case's prj.conf file.

Signed-off-by: Lixin Guo <8de84fecf2daa12e9dd27dd0d7f47ee7775a73c0@intel.com>

zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr