Test pcc and python3-pcpp for /usr/bin/pcpp

[yashi]

Ubuntu / Debian has a package, pcc, with an executable named /usr/bin/pcpp.

https://packages.ubuntu.com/noble/amd64/pcc/filelist

It also has python3-pcpp, which installs /usr/bin/pcpp-python instead of pcpp.

petalinux-env-check doesn't check the fact above and let lopper run pcpp.

Lopper checks an environment variable LOPPER_CPP and if it's not set then it shutil.which("pcpp").
https://github.com/devicetree-org/lopper/blob/6b8e26d4bda607d96ad738764d734a177be02c0a/lopper/base.py#L114

petalinux-build should check the package pcc installed or not, or set LOPPER_CPP to python pcpp. Or at least the doc should mention this fact.