rwlock: add HTM lock elision for x86

rwlock: add HTM lock elision for x86

This patch adds methods that use hardware memory transactions (HTM) on
fast-path for rwlock (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 rwlock if HTM is not available or memory transactions fail. This is
not a replacement for all rwlock usages since not all critical sections
protected by locks 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>