dt-bindings: eeprom: at24: Fix ST M24C64-D compatible schema

The schema for the ST M24C64-D compatible string doesn't work.
Validation fails as the 'd-wl' suffix is not added to the preceeding
schema which defines the entries and vendors. The actual users are
incorrect as well because the vendor is listed as Atmel whereas the
part is made by ST.

As this part doesn't appear to have multiple vendors, move it to its own
entry.

Fixes: 0997ff1f ("dt-bindings: at24: add ST M24C64-D Additional Write lockable page")
Fixes: c761068f ("dt-bindings: at24: add ST M24C32-D Additional Write lockable page")
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Marek Vasut <marex@denx.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>