sm501: Add panel hardware cursor registers also to read function

These were forgotten when adding panel layer support in ffd39257
"SM501 emulation for R2D-SH4".

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
[dwg: Added reference to earlier commit in message]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>