x86: qemu: qfw: Implement acpi_get_rsdp_addr()

U-Boot on QEMU does not build ACPI table by ourself, instead it uses
the prebuilt ACPI table via the qfw interface. This implements the
qfw version of acpi_get_rsdp_addr() for setup_zimage().

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/misc/qfw.c

@@ -222,6 +222,14 @@ out:
 	free(table_loader);
 	return addr;
 }
+
+ulong acpi_get_rsdp_addr(void)
+{
+	struct fw_file *file;
+
+	file = qemu_fwcfg_find_file("etc/acpi/rsdp");
+	return file->addr;
+}
 #endif
 
 /* Read configuration item using fw_cfg PIO interface */