i2c: core: Use DEVICE_ATTR_*() helper macros

Convert the i2c core sysfs attributes from DEVICE_ATTR() to
DEVICE_ATTR_*(), to reduce boilerplate.
This requires renaming some functions.

Although no suitable macro exists for the delete_device attribute,
rename i2c_sysfs_delete_device() to delete_device_store() for
consistency.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>