Allow TCG plugins to read memory
Additional information:
* `include/qemu/plugin.h`
* `include/qemu/qemu-plugin.h`
* `plugin/api.c`

PANDA implemented this already (not sure if this solution is acceptable for the mainline QEMU): https://github.com/qemu/qemu/commit/72c661a7f141ab41fbce5e95eb3593b69f40e246