x86: bootm: Fix FIT image booting on x86

Checking 'is_zimage' at this time will always fail and therefore booting
a FIT style image will always lead to this error message:

"## Kernel loading failed (missing x86 kernel setup) ..."

This change now removes this check and booting of FIT images works just
fine.
Signed-off-by: NStefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>

arch/x86/lib/bootm.c

@@ -100,7 +100,7 @@ static int boot_prep_linux(bootm_headers_t *images)
 		}
 		is_zimage = 1;
 #if defined(CONFIG_FIT)
-	} else if (images->fit_uname_os && is_zimage) {
+	} else if (images->fit_uname_os) {
 		ret = fit_image_get_data(images->fit_hdr_os,
 				images->fit_noffset_os,
 				(const void **)&data, &len);