sim/m32r: return register sizes after fetch and store

sim/m32r: return register sizes after fetch and store

The m32r simulator currently always returns -1 for the register size
after both a fetch and a store.  In the fetch case GDB is forgiving of
this, but in the store case GDB treats a return value of -1 as an
error.

This commit updates the m32r simulator to return a valid register size
when fetching or storing a register.  This fixes any GDB test that
writes to a register, which will include any GDB test that makes an
inferior call, for example gdb.base/break.exp.

sim/m32r/ChangeLog:

	* m32r.c (m32rbf_register_size): New function.
	(m32rbf_fetch_register): Use new function.
	(m32rbf_store_register): Likewise.