net: cadence_gem: Clean up variable names

net: cadence_gem: Clean up variable names

Cleanup some variable names in preparation for migrating the state
struct and type cast macro to a public header. The acronym "GEM" on
its own is not specific enough to be used in a more global namespace
so preface with "cadence". Fix the capitalisation of "gem" in the
state type while touching the typename. Also preface the GEM_MAXREG
macro as this will need to migrate to public header.

Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Tested-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 8e2b0687b3a7b7a3fde5ba2f3bee6f3b911e84ef.1431381507.git.peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>