[Request] Instead of setting linux_cachyos, assert AMD_PRIVATE_COLOR for HDR

[PedroHLC]

What happens?

Presently, chaotic.hdr sets kernel to linux_cachyos. But HDR has been merged into Linux 6.8, so this is not needed anymore. Instead, we want any 6.8+ kernel built with -DAMD_PRIVATE_COLOR in KCFLAGS.

What is expected to happen?

If the user has an LTS kernel, he should be warned that it does not support HDR, and advised to upgrade to either 6.8+ with AMD_PRIVATE_COLOR or linux_cachyos (needs rebuild with AMD_PRIVATE_COLOR rn).