dt-bindings: vendor-prefixes: clarify HP prefix

There are two independent companies: "HP Inc." and "Hewlett Packard
Enterprise". Clarify that "hp" prefix is about the first one.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220127075229.10299-1-krzysztof.kozlowski@canonical.com