bios_emulator: Add Kconfig and adjust Makefile for SPL

The Kconfig for this is currently inside a particular board. Move it into
the correct place and allow use in SPL, so that video can be used there
if needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/Makefile b/drivers/Makefile
index 78dcf62..3bc6d27 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0+
 
+obj-$(CONFIG_$(SPL_TPL_)BIOSEMU) += bios_emulator/
 obj-$(CONFIG_$(SPL_TPL_)BLK) += block/
 obj-$(CONFIG_$(SPL_TPL_)BOOTCOUNT_LIMIT) += bootcount/
 obj-$(CONFIG_$(SPL_TPL_)BUTTON) += button/
@@ -80,7 +81,6 @@
 obj-y += adc/
 obj-y += ata/
 obj-$(CONFIG_DM_DEMO) += demo/
-obj-$(CONFIG_BIOSEMU) += bios_emulator/
 obj-y += block/
 obj-y += cache/
 obj-$(CONFIG_CPU) += cpu/