eal: replace libc-based random generation with LFSR

This commit replaces rte_rand()'s use of lrand48() with a DPDK-native
combined Linear Feedback Shift Register (LFSR) (also known as
Tausworthe) pseudo-random number generator.

This generator is faster and produces better-quality random numbers
than the linear congruential generator (LCG) of lib's lrand48(). The
implementation, as opposed to lrand48(), is multi-thread safe in
regards to concurrent rte_rand() calls from different lcore threads.
A LCG is still used, but only to seed the five per-lcore LFSR
sequences.

In addition, this patch also addresses the issue of the legacy
implementation only producing 62 bits of pseudo randomness, while the
API requires all 64 bits to be random.

This pseudo-random number generator is not cryptographically secure -
just like lrand48().

Bugzilla ID: 114
Bugzilla ID: 276

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>