m32r: relocate drivers back out of 8250 dir

Commit 9bef3d4197379a995fa80f81950bbbf8d32e9e8b

"serial: group all the 8250 related code together"

inadvertently swept up the m32r driver in the move, because
it had comments mentioning 8250 registers within it. However
these are only there by nature of the driver being based off
the 8250 source code -- the hardware itself does not actually
have any relation to the original 8250 style UARTs.

Reported-by: Jiri Slaby <[e-mail]>
Signed-off-by: Paul Gortmaker <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>