plugins: extend execlog to filter matches

plugins: extend execlog to filter matches

Sometimes the whole execlog is just two much so add the ability to
filter by instruction opcode or address.

[AJB: this shows for example

 qemu-system-aarch64 -display none -serial mon:stdio \
   -M virt -cpu max \
   -semihosting-config enable=on \
   -kernel ./tests/tcg/aarch64-softmmu/memory-sve \
   -plugin ./contrib/plugins/libexeclog.so,ifilter=st1w,afilter=0x40001808 -d plugin -D plugin.out

the st1w SVE instruction is not instrumenting its stores.]

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alexandre Iooss <erdnaxe@crans.org>
Cc: Robert Henry <robhenry@microsoft.com>
Cc: Aaron Lindsay <aaron@os.amperecomputing.com>
Message-Id: <20220929114231.583801-36-alex.bennee@linaro.org>