gateware: Wrap capture/counter units and allow use of SB_MAC16

We have a bunch of Multiply Add units that are un-used, we can
make use of the "accumulate" part to implement the few wide
counters we have to win some LCs.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/gateware/icE1usb/Makefile b/gateware/icE1usb/Makefile
index ca1698a..759896f 100644
--- a/gateware/icE1usb/Makefile
+++ b/gateware/icE1usb/Makefile
@@ -11,6 +11,8 @@
 	sysmgr.v \
 )
 PROJ_RTL_SRCS += $(addprefix ../common/rtl/, \
+	capcnt.v \
+	capcnt_sb_mac16.v \
 	dfu_helper.v \
 	picorv32.v \
 	picorv32_ice40_regs.v \