arch/acpi.h: Use of typedef for acpi_vfct_image_hdr

Use of typedef and modify the usage accordingly.

Change-Id: I65581702a60dbd286cb3910c6eeef5f9e1853cf1
Signed-off-by: Himanshu Sahdev <himanshusah@hcl.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36184
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Richard Spiegel <richard.spiegel@silverbackltd.com>

src/device/pci_rom.c

@@ -200,7 +200,7 @@ static unsigned long
 pci_rom_acpi_fill_vfct(struct device *device, struct acpi_vfct *vfct_struct,
 		       unsigned long current)
 {
-	struct acpi_vfct_image_hdr *header = &vfct_struct->image_hdr;
+	acpi_vfct_image_hdr_t *header = &vfct_struct->image_hdr;
 	struct rom_header *rom;
 
 	rom = check_initialized(device);