gas/riscv: Remove unneeded structure

gas/riscv: Remove unneeded structure

We build a hash table of all register classes and numbers.  The hash
key is the register name and the hash value is the class and number
encoded into a single value, which is of type 'void *'.

When we pull the values out of the hash we cast them to be a pointer
to a structure, however, we never access the fields of that structure,
we just decode the register class and number from the pointer value
itself.

This commit removes the structure and treats the encoded class and
number as a 'void *' during hash lookup.

gas/ChangeLog:

	* config/tc-riscv.c (struct regname): Delete.
	(hash_reg_names): Handle value as 'void *'.

Change-Id: Ie7d8f46ca3798f56f4af94395279de684f87f9cc