eal: fix pedantic build of mlx4 debug mode

eal: fix pedantic build of mlx4 debug mode

Since the commit below includes rte_cpuflags.h in rte_spinlock.h,
compilation of the mlx4 driver fails when CONFIG_RTE_LIBRTE_MLX4_DEBUG=y.

This mode adds -pedantic to the compiler's command line for mlx4, which
complains about the static definition of an empty cpu_feature_table[] in
common rte_cpuflags.h, then about its redefinition as a larger array in
arch-specific rte_cpuflags.h.

While DPDK does not officially support -pedantic internally, external
applications may enable it and include rte_spinlock.h from the public API.

Instead of removing -pedantic from mlx4, this commit fixes rte_cpuflags.h.

Fixes: ba7468997ea6 ("spinlock: add HTM lock elision for x86")

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: David Marchand <david.marchand@6wind.com>