dt-bindings: memory: lpddr3: adjust IO width to spec

According to JEDEC Standard No. 209-3 (table 3.4.1 "Mode Register
Assignment and Definition in LPDDR3 SDRAM"), the LPDDR3 supports only
16- and 32-bit IO width.  Drop the unsupported others.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220206135807.211767-5-krzysztof.kozlowski@canonical.com

Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr3.yaml

@@ -34,10 +34,8 @@ properties:
     description: |
       IO bus width in bits of SDRAM chip.
     enum:
-      - 64
       - 32
       - 16
-      - 8
 
   manufacturer-id:
     $ref: /schemas/types.yaml#/definitions/uint32