boards: x86: fix KERNEL_VM_SIZE for QEMU if ACPI
boards: x86: fix KERNEL_VM_SIZE for QEMU if ACPI

The default KERNEL_VM_SIZE if ACPI=y is too large for QEMU targets
which results in page tables being too big to fit in available
memory. So limit the VM size to a more reasonable one.

Signed-off-by: Daniel Leung <d94e04d205b5962d7873a139ef298b03c1717f72@intel.com>

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