x86/virt, x86/acpi: Add test for ACPI_FADT_NO_VGA

Add a test for ACPI_FADT_NO_VGA when scanning the FADT and set the new
flag x86_platform.legacy.no_vga accordingly.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: len.brown@intel.com
Cc: linux-pm@vger.kernel.org
Cc: pavel@ucw.cz
Cc: rjw@rjwysocki.net
Link: http://lkml.kernel.org/r/20171109132739.23465-4-jgross@suse.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>