[mlir] fix polynomial dialect docs

Some docs were emitted into the wrong location (Polynomial/ instead of
Dialect/). Furthermore, `-gen-dialect-docs` subsumes
`-gen-attr/typedef-docs` so the latter are not required.

Add a top-level entry that includes both other files in a proper order.

Author: ftynse

mlir/docs/Dialects/Polynomial.md

@@ -0,0 +1,2 @@
+[include "Dialects/PolynomialDialect.td"]
+[include "Dialects/PolynomialOps.td"]

mlir/include/mlir/Dialect/Polynomial/IR/CMakeLists.txt

@@ -1,8 +1,6 @@
 add_mlir_dialect(Polynomial polynomial)
-add_mlir_doc(Polynomial PolynomialDialect Polynomial/ -gen-dialect-doc -dialect=polynomial)
-add_mlir_doc(Polynomial PolynomialOps Polynomial/ -gen-op-doc)
-add_mlir_doc(Polynomial PolynomialAttributes Dialects/ -gen-attrdef-doc)
-add_mlir_doc(Polynomial PolynomialTypes Dialects/ -gen-typedef-doc)
+add_mlir_doc(Polynomial PolynomialDialect Dialects/ -gen-dialect-doc -dialect=polynomial)
+add_mlir_doc(Polynomial PolynomialOps Dialects/ -gen-op-doc)
 
 set(LLVM_TARGET_DEFINITIONS Polynomial.td)
 mlir_tablegen(PolynomialAttributes.cpp.inc -gen-attrdef-defs -attrdefs-dialect=polynomial)