platform/x86: firmware_attributes_class: Move include linux/device/class.h

platform/x86: firmware_attributes_class: Move include linux/device/class.h

The header firmware_attributes_class.h uses 'struct class'. It should
also include the necessary dependency header.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Tested-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Link: https://lore.kernel.org/r/20250104-firmware-attributes-simplify-v1-1-949f9709e405@weissschuh.net
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>