platform: thinkpad_acpi: convert to use DRIVER_ATTR_RO/RW

We are trying to get rid of DRIVER_ATTR(), and the thinkpad_acpi
driver's attributes can be trivially changed to use DRIVER_ATTR_RO() and
DRIVER_ATTR_RW().

Cc: Henrique de Moraes Holschuh <ibm-acpi@hmh.eng.br>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: <ibm-acpi-devel@lists.sourceforge.net>
Cc: <platform-driver-x86@vger.kernel.org>
Reviewed-by: Darren Hart (VMware) <dvhart@infradead.org>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>