x86: qemu: split qfw command interface and qfw core

This patch splits qfw command interface and qfw core function into two
files, and introduces a new Kconfig option (CONFIG_QFW) for qfw core.

Now when qfw command interface is enabled, it will automatically select
qfw core. This patch also makes the ACPI table generation select
CONFIG_QFW.

Signed-off-by: Miao Yan <yanmiaobest@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index af8667f..fa53700 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -138,4 +138,10 @@
 	  legacy UART or other devices in the Winbond Super IO chips
 	  on X86 platforms.
 
+config QFW
+	bool
+	help
+	  Hidden option to enable QEMU fw_cfg interface. This will be selected by
+	  either CONFIG_CMD_QEMU_FW_CFG or CONFIG_GENERATE_ACPI_TABLE.
+
 endmenu