nvenc: Improve negotiation with upstream interlace-mode and downstream profile

nvenc: Return profile compatible input formats from GstVideoEncoder::getcaps

Do not accept any input formats which could not be supported
downstream requested codec profiles.

nvenc: Fix caps negotiation failure on unspecified interlace-mode

During GstVideoInfo conversion from GstCaps, interlace-mode is
inferred to progressive so unspecified interlace-mode should not cause any
negotiation issue.

nvenc: Remove unused member variables

Supported interlace-mode and codec profiles are checked
during plugin init and those values are never used.

tests: nvenc: Add test caps negotiation with interlace-mode field