Mk/**ocaml.mk: Convert remaining bsd.ocaml.mk to Uses/ocaml.mk

• Instead of USE_OCAML=yes use USES=ocaml. If empty USES=ocaml implies build and run
• Instead of USE_OCAMLFIND_PLIST use USES=ocaml:findplist which also implies USES=ocaml:findlib
• Instead of USE_OCAML_CAMLP4 use USES=ocaml:camlp4
• Instead of USE_OCAML_FINDLIB use USES=ocaml:findlib
• Instead of USE_OCAML_LDCONFIG use USES=ocaml:ldconfig
• Instead of USE_OCAML_WASH use USES=ocaml:wash
• Instead of NO_OCAML_BUILDDEPENDS use USES=ocaml:run
• Instead of NO_OCAML_RUNDDEPENDS use USES=ocaml:build
• Instead of USE_OCAML_TK use USES=ocaml:tk which actually implies USES=ocaml:tkbuild and USES=ocaml:tkrun
• Instead of NO_OCAMLTK_BUILDDEPENDS use USES=ocaml:tkrun
• Instead of NO_OCAMLTK_RUNDEPENDS use USES=ocaml:tkbuild
• USES=ocaml:dune remains unchanged
• Prepare to add/remove keywords easily

Approved by: mat (portmgr)
Reviewed by: freebsd@dev.thsi.be
Differential Revision: https://reviews.freebsd.org/D48227