log: introduce logtype register macro

Introduce the RTE_LOG_REGISTER macro to avoid the code duplication
in the logtype registration process.

It is a wrapper macro for declaring the logtype, registering it and
setting its level in the constructor context.

Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: Adam Dybkowski <adamx.dybkowski@intel.com>
Acked-by: Sachin Saxena <sachin.saxena@nxp.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>