treewide: Fix default num. of AXI-REALM managers and regenerate regs

This parameter in the makefrag affects the number of registers generated
inside the AXI-REALM IP. The default value, associated with the default
configuration of Cheshire, is 6, accounting for: `core0`, `debug
module`, `dma`, `serial link`, `vga` and `usb`. Change accordingly if
the configuration changes, e.g., the number of cores or if new managers
are added.

cheshire.mk

@@ -96,7 +96,7 @@ $(OTPROOT)/.generated: $(CHS_ROOT)/hw/rv_plic.cfg.hjson
 	flock -x $@ sh -c "cp $< $(dir $@)/src/rv_plic/; $(MAKE) -j1 otp" && touch $@
 
 # AXI RT
-AXIRT_NUM_MGRS ?= 8
+AXIRT_NUM_MGRS ?= 6
 AXIRT_NUM_SUBS ?= 2
 include $(AXIRTROOT)/axirt.mk
 $(AXIRTROOT)/.generated: