plugins/howvec: adapting to the new argument passing scheme

Correctly parsing plugin argument since they now must be provided as
full-form boolean parameters, e.g.:
    -plugin ./contrib/plugins/libhowvec.so,verbose=on,inline=on

Also, introduced the argument "count" that accepts one opt to count
individually at a time.

Signed-off-by: Mahmoud Mandour <ma.mandourr@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210730135817.17816-8-ma.mandourr@gmail.com>

docs/devel/tcg-plugins.rst

@@ -80,7 +80,7 @@ Once built a program can be run with multiple plugins loaded each with
 their own arguments::
 
   $QEMU $OTHER_QEMU_ARGS \
-      -plugin tests/plugin/libhowvec.so,arg=inline,arg=hint \
+      -plugin tests/plugin/libhowvec.so,inline=on,count=hint \
       -plugin tests/plugin/libhotblocks.so
 
 Arguments are plugin specific and can be used to modify their
@@ -212,13 +212,13 @@ The hotpages plugin can be configured using the following arguments:
 
 This is an instruction classifier so can be used to count different
 types of instructions. It has a number of options to refine which get
-counted. You can give an argument for a class of instructions to break
-it down fully, so for example to see all the system registers
-accesses::
+counted. You can give a value to the `count` argument for a class of
+instructions to break it down fully, so for example to see all the system
+registers accesses::
 
   ./aarch64-softmmu/qemu-system-aarch64 $(QEMU_ARGS) \
     -append "root=/dev/sda2 systemd.unit=benchmark.service" \
-    -smp 4 -plugin ./contrib/plugins/libhowvec.so,arg=sreg -d plugin
+    -smp 4 -plugin ./contrib/plugins/libhowvec.so,count=sreg -d plugin
 
 which will lead to a sorted list after the class breakdown::