acpi: Disable ACPI table override if securelevel is set

From the kernel documentation (initrd_table_override.txt):

  If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible
  to override nearly any ACPI table provided by the BIOS with an
  instrumented, modified one.

When securelevel is set, the kernel should disallow any unauthenticated
changes to kernel space. ACPI tables contain code invoked by the kernel, so
do not allow ACPI tables to be overridden if securelevel is set.

Signed-off-by: Linn Crosetto <linn@hpe.com>
u64 acpi_os_get_timer(void)
{
	u64 time_ns = ktime_to_ns(ktime_get());
	do_div(time_ns, 100);
	return time_ns;
}

u64 acpi_os_get_timer(void)
{
	u64 time_ns = ktime_to_ns(ktime_get());
	do_div(time_ns, 100);
	return time_ns;
}
