acpi: Enable ACPI table generation by default on x86

This should ideally be used by all x86 boards in U-Boot. Enable it by
default. If some boards don't use it, the cost is small.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/Kconfig b/arch/Kconfig
index a11f872..9be02d1 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -190,6 +190,7 @@
 	imply PCH
 	imply RTC_MC146818
 	imply IRQ
+	imply ACPIGEN if !QEMU
 
 	# Thing to enable for when SPL/TPL are enabled: SPL
 	imply SPL_DM