qemu: update 7.1.0 -> 7.2.0

qemu no longer carries libslirp in-tree,
so enabling slirp requires providing external libslirp.

Another noteworthy change is:

x86: TCG support for AVX, AVX2, F16C, FMA3 and VAES instructions

... which means both meta-intel and qemu x86 targets can
now fully utilize Haswell-and-later instruction set with benefits
for performance in emulation and on silicon.

Changelog:
https://wiki.qemu.org/ChangeLog/7.2



Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>