nvmem: meson-efuse: indicate that this driver is only for Meson GX SoCs

The current Amlogic Meson eFuse driver only supports the 64-bit SoCs
(GXBB and newer). Older SoCs cannot be supported by the same driver
because they do not use the meson secure monitor firmware to access the
hardware.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>