Intel GPU: psr and fbc should not be manually set for >7th GPU gen, and be manually enabled for GPU gen 6-7.5

[ahydronous]

Framebuffer Compression (fbc) is supported for Sandy Bridge (6th) GPU generation and beyond. However, it sometimes bugs out with earlier generations if set with psr mode 2. 1 works.

Broadwell (8th) GPU generation and beyond automatically enable these options (value -1) since kernel 4.18, and thus also manage any issues between fbc and psr.