spinlock: add HTM lock elision for x86

spinlock: add HTM lock elision for x86

This patch adds methods that use hardware memory transactions (HTM) on fast-path
for spinlocks (a.k.a. lock elision). Here the methods are implemented for x86
using Restricted Transactional Memory instructions (Intel(r) Transactional
Synchronization Extensions). The implementation fall-backs to the normal
spinlock if HTM is not available or memory transactions fail. This is not
a replacement for all spinlock usages since not all critical sections protected
by spinlocks are friendly to HTM. For example, an attempt to perform a HW I/O
operation inside a hardware memory transaction always aborts the transaction
since the CPU is not able to roll-back should the transaction fail.
Therefore, hardware transactional locks are not advised to be used around
rte_eth_rx_burst() and rte_eth_tx_burst() calls.

Signed-off-by: Roman Dementiev <roman.dementiev@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>