media: venus: core: Add differentiator IS_V6(core)

This commit adds the macro helper IS_V6() which will be used to
differentiate iris2/v6 silicon from previous versions.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>