pld: add support for cologne chip gatemate fpgas

Change-Id: I0bf5a52ee6a7f0287524619114eba0cfccf6ac81
Signed-off-by: Daniel Anselmi <danselmi@gmx.ch>
Reviewed-on: https://review.openocd.org/c/openocd/+/7565
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

doc/openocd.texi

@@ -8566,6 +8566,12 @@ The files @verb{|.fs|} and @verb{|.bin|} generated by Gowin FPGA Designer are su
 @end deffn
 
 
+@deffn {FPGA Driver} {gatemate}
+This driver can be used to load the bitstream into GateMate FPGAs form CologneChip.
+The files @verb{|.bit|} and @verb{|.cfg|} both generated by p_r tool from CologneChip are supported.
+@end deffn
+
+
 @node General Commands
 @chapter General Commands
 @cindex commands