dp8393x: Rewrite dp8393x_get() / dp8393x_put()

dp8393x: Rewrite dp8393x_get() / dp8393x_put()

Instead of accessing N registers via a single address_space API
call using a temporary buffer (stored in the device state) and
updating each register, move the address_space call in the
register put/get. The load/store and word size checks are moved
to put/get too. This simplifies a bit, making the code easier
to read.

Co-developed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Co-developed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Finn Thain <fthain@linux-m68k.org>
Message-Id: <20210710174954.2577195-8-f4bug@amsat.org>