m48t59: register a QOM type for each nvram type we support

m48t59: register a QOM type for each nvram type we support

As m48t59 devices can only be created with m48t59_init() or m48t59_init_isa(),
we know exactly which nvram types are required. Register only those three
types.

Remove .model and .size properties as they can be infered from nvram name.

Rename type to 'isa-*' (and 'sysbus-*') to do like other devices ISA devices
(isa-ide, isa-parallel, isa-serial...)

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
CC: Andreas Färber <afaerber@suse.de>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>