Allow building XVC client without libftdi.

Unlike the XVC server, the XVC client does not depend on libftdi, so
building it just depends on having separate flags for enabling it.

src/jtag.cpp

@@ -55,7 +55,7 @@
 #ifdef ENABLE_USBBLASTER
 #include "usbBlaster.hpp"
 #endif
-#ifdef ENABLE_XVC
+#ifdef ENABLE_XVC_CLIENT
 #include "xvc_client.hpp"
 #endif
 
@@ -186,7 +186,7 @@ Jtag::Jtag(const cable_t &cable, const jtag_pins_conf_t *pin_conf,
 		throw std::exception();
 #endif
 	case MODE_XVC_CLIENT:
-#ifdef ENABLE_XVC
+#ifdef ENABLE_XVC_CLIENT
 		_jtag = new XVC_client(ip_adr, port, clkHZ, verbose);
 		break;
 #else