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/cmd/Kconfig b/cmd/Kconfig
index c0fffe3..08b761f 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -596,6 +596,7 @@
 config CMD_QEMU_FW_CFG
 	bool "qfw"
 	depends on X86
+	select QFW
 	help
 	  This provides access to the QEMU firmware interface.  The main
 	  feature is to allow easy loading of files passed to qemu-system