eal: introduce macro for always inline

eal: introduce macro for always inline

Different drivers use internal macros like force_inline for compiler
always inline feature.
Standardizing it through __rte_always_inline macro.

Verified the change by comparing the output binary file.
No difference found in the output binary file with this change.

Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>