tcl: Support for the miniSpartan6+ board.

* https://www.scarabhardware.com/minispartan6/
 * https://github.com/scarabhardware/miniSpartan6-plus/raw/master/miniSpartan6%2B_Rev_B.pdf

The miniSpartan6+ board is wired identically to the Pipistrello device but
sadly doesn't have a custom device description.

Change-Id: I07fd57b1ec87d72edf68860684928a3781e2f08a
Signed-off-by: Tim 'mithro' Ansell <mithro@mithis.com>
Reviewed-on: http://openocd.zylin.com/3117
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>

tcl/board/minispartan6.cfg

@@ -0,0 +1,24 @@
+# https://www.scarabhardware.com/minispartan6/
+
+source [find interface/ftdi/minispartan6.cfg]
+source [find cpld/xilinx-xc6s.cfg]
+source [find cpld/jtagspi.cfg]
+
+# example command to read the device dna of the FPGA on the board;
+# openocd -f board/minispartan6.cfg -c "init;xc6s_print_dna xc6s.tap;shutdown"
+
+# example command to write bitstream
+# openocd -f board/minispartan6.cfg -c "init;\
+# jtagspi_init 0 bscan_spi_xc6slx??.bit;\
+# jtagspi_program bitstream.bin 0;\
+# xc6s_program xc6s.tap;\
+# shutdown"
+#
+# jtagspi flash procies can be found in the contrib/loaders/flash/fpga/
+# directory, with prebuilt versions available at
+# https://github.com/jordens/bscan_spi_bitstreams
+#
+# For the SLX25 variant, use
+#  - https://github.com/jordens/bscan_spi_bitstreams/raw/master/bscan_spi_xc6slx25.bit
+# For the SLX9 variant, use
+#  - https://github.com/jordens/bscan_spi_bitstreams/raw/master/bscan_spi_xc6slx9.bit

tcl/interface/ftdi/minispartan6.cfg

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+# https://www.scarabhardware.com/minispartan6/
+# https://github.com/scarabhardware/miniSpartan6-plus/raw/master/miniSpartan6%2B_Rev_B.pdf
+interface ftdi
+# The miniSpartan6+ sadly doesn't have a custom device description, so we just
+# have to hope you got it right.
+#ftdi_device_desc "Dual RS232-HS"
+ftdi_vid_pid 0x0403 0x6010
+# interface 1 is the uart
+ftdi_channel 0
+# just TCK TDI TDO TMS, no reset
+ftdi_layout_init 0x0008 0x000b
+reset_config none
+# this generally works fast: the fpga can handle 30MHz, the spi flash can handle
+# 54MHz with simple read, no dummy cycles, and wait-for-write-completion
+adapter_khz 30000