hpdcache: move `hpdcache_nline_t` type declaration in module definition

This PR changes hpdcache_nline_t from a parameter internal to the HPDCache to an external definition. This is needed to comply with OpenPiton invalidation interface, as it is relies on a top level signal using this data type. https://github.com/openhwgroup/cv-hpdcache/blob/66b29242b8a1bf95e88b606d39a8873de3c899ba/rtl/src/hpdcache.sv#L99