ethdev: refine debug build option

ethdev: refine debug build option

PMDs use RTE_LIBRTE_<PMD_NAME>_DEBUG_RX|TX as build option to wrap
data path debug code. As .config has been removed since the meson build,
It is not friendly for new DPDK users to notice those debug options.

The patch introduces below build options for data path debug, so PMD
can choose to reuse them to avoid maintain their own.

- RTE_ETHDEV_DEBUG_RX
- RTE_ETHDEV_DEBUG_TX

All the build options are documented at programming guide
"3.1 Driver Option", so users can easily find them.

The original undocumented RTE_LIBRTE_ETHDEV_DEBUG will alias to
both RTE_ETHDEV_DEBUG_RX and RTE_ETHDEV_DEBUG_TX for backward
compatibility.

Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>