emulators/qemu: Enable virtfs support

v10.2.0 contains the commit which enables 9p support on freebsd.

https://gitlab.com/qemu-project/qemu/-/commit/6657f3bb55edba8f068cbc9ac40bb230ea1d7a09,

Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D54541