Improve configuration of FPGA subsystem

This patch removes the FPGA subsystem configuration through
the CONFIG_FPGA bitmask configuration option.

See README for the new options:

	CONFIG_FPGA,
	CONFIG_FPGA_<vendor>,
	CONFIG_FPGA_<family>

Signed-off-by: Matthias Fuchs <matthias.fuchs@esd-electronics.com>
diff --git a/common/virtex2.c b/common/virtex2.c
index b5dc366..1283ff6 100644
--- a/common/virtex2.c
+++ b/common/virtex2.c
@@ -31,7 +31,7 @@
 #include <common.h>
 #include <virtex2.h>
 
-#if (CONFIG_FPGA & (CFG_XILINX | CFG_VIRTEX2))
+#if defined(CONFIG_FPGA) && defined(CONFIG_FPGA_VIRTEX2)
 
 #if 0
 #define FPGA_DEBUG