eal/x86: check rdrand and rdseed

eal/x86: check rdrand and rdseed

The meson build never checked for the presence of rdrand and rdseed
instructions, while make build never checked for rdseed. Ensure builds
always have the appropriate checks - and therefore defines - for these
instructions. For runtime, we also add in rdseed to the list of known
bits returned from cpuid() instruction, so we can confirm its presence at
application init time.

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