reexporting all the BMCR_ values by hand doesn't sound fun. Can we
automaticall generate such?

The C22 address space only have a max of 32, and no more are expected.

C45 address space can have in theory 32 x 65536, although in practice
it is sparsely populated. But new values are added every so often. So
generated at build time from the #defines would be better.

	  Andrew