AM64 SoC contains the GPMC module. Add compatible for it.

Newer SoCs don't necessarily map GPMC data region at the same place
as legacy SoCs. Add reg-names "data", to provide this information to
the device driver.
Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211221131757.2030-2-rogerq@kernel.orgSigned-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>