aarch64: Handle V4BF V8BF modes in vwcore attribute

aarch64: Handle V4BF V8BF modes in vwcore attribute

While playing with other unrelated changes I hit an assemble-failure bug where
a pattern (one of the get_lane ones) that was using V4BF, V8BF as part of a
mode iterator and outputting registers with the vwcore attribute,
but there is no vwcore mapping for V4BF and V8BF.

This patch fixes that in the obvious way by adding the missing mappings

Bootstrapped and tested on aarch64-none-linux-gnu.

gcc/ChangeLog:

	* config/aarch64/iterators.md (vwcore): Handle V4BF, V8BF.