fpga: Protect GZIP usage when LOADMK is enabled

For case where CMD_FPGA_LOADMK is enabled and GZIP disable.

Warning log:
common/built-in.o: In function `do_fpga':
/mnt/disk/u-boot/common/cmd_fpga.c:218: undefined reference to `gunzip'

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/cmd_fpga.c b/common/cmd_fpga.c
index 8c5bf44..484a6c6 100644
--- a/common/cmd_fpga.c
+++ b/common/cmd_fpga.c
@@ -211,6 +211,7 @@
 
 				comp = image_get_comp(hdr);
 				if (comp == IH_COMP_GZIP) {
+#if defined(CONFIG_GZIP)
 					ulong image_buf = image_get_data(hdr);
 					data = image_get_load(hdr);
 					ulong image_size = ~0UL;
@@ -222,6 +223,10 @@
 						return 1;
 					}
 					data_size = image_size;
+#else
+					puts("Gunzip image is not supported\n");
+					return 1;
+#endif
 				} else {
 					data = (ulong)image_get_data(hdr);
 					data_size = image_get_data_size(hdr);