test/memcpy_perf: provide perf ratio and test time

The printed time values presented in TSC is not straight forward
showing the performance difference.  And if the high resolution
counter is not enabled, time value is too small to show the actual
performance (e.g. "1 - 1" seems the same but in fact the perfomance
diffs by 50% or more).
With the performance difference ratio caculated and printed, it'll be
easier for people to read and compare the performance between
rte_memcpy() and memcpy().
Since the TSC values' units may diff a lot on different platforms,
the total execution time of aligned/unaligned memcpy test are
provided to allow comparation between platforms.

Signed-off-by: Herbert Guan <herbert.guan@arm.com>
Acked-by: Jianbo Liu <jianbo.liu@arm.com>