tests/benchmarks/boot_time: disable on QEMU targets
tests/benchmarks/boot_time: disable on QEMU targets

These all currently use the HPET timer, and thus can't build with
BOOT_TIME_MEASUREMENT enabled, so disable for now. This test is
basically a build-only test, so we're covered with the other x86
targets (gpmrb, up_squared) for now.

Signed-off-by: Charles E. Youse <5bc2c6f24e92b68873229a004438f1d6a77a3862@intel.com>

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