firmware: turris-mox-rwtm: Don't create own kobject type

firmware: turris-mox-rwtm: Don't create own kobject type

In order to create attribute files in /sys/firmware/turris-mox-rwtm,
this driver creates it's own kobject type.

Simplify this by dropping this own kobject creation, and instead
creating standard device attribute files.

For backwards compatibility with sysfs ABI, create a symlink
/sys/firmware/turris-mox-rwtm, pointing to this device's sysfs
directory.

Signed-off-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20240831092050.23093-8-kabel@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>