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/README b/README
index 26f93c2..9a8b3b9 100644
--- a/README
+++ b/README
@@ -1377,14 +1377,23 @@
 		SPI configuration items (port pins to use, etc). For
 		an example, see include/configs/sacsng.h.
 
-- FPGA Support: CONFIG_FPGA_COUNT
+- FPGA Support: CONFIG_FPGA
 
-		Specify the number of FPGA devices to support.
+		Enables FPGA subsystem.
+
+		CONFIG_FPGA_<vendor>
+
+		Enables support for specific chip vendors.
+		(ALTERA, XILINX)
 
-		CONFIG_FPGA
+		CONFIG_FPGA_<family>
 
-		Used to specify the types of FPGA devices.  For example,
-		#define CONFIG_FPGA  CFG_XILINX_VIRTEX2
+		Enables support for FPGA family.
+		(SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)
+
+		CONFIG_FPGA_COUNT
+
+		Specify the number of FPGA devices to support.
 
 		CFG_FPGA_PROG_FEEDBACK