dt-bindings: memory: lpddr2: Document Elpida B8132B2PB-6D-F

Elpida B8132B2PB-6D-F memory chip is used by ASUS Transformer TF101
tablet, add compatible for it. We need to specify this compatible it
for a device-tree node containing corresponding memory timings in order
to allow software to match the timings with the detected hardware.
Signed-off-by: NDmitry Osipenko <digetx@gmail.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211006224659.21434-5-digetx@gmail.comSigned-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr2.yaml

@@ -15,6 +15,7 @@ properties:
       - items:
           - enum:
               - elpida,ECB240ABACN
+              - elpida,B8132B2PB-6D-F
           - enum:
               - jedec,lpddr2-s4
       - items: