common: expose true random number generator API
common: expose true random number generator API

When supported, the true random number generator provide to API calls,
to initialize it and to retrieve a random number.

BRANCH=none
BUG=chrome-os-partner:43025
TEST=with other patches in place TPM2 gets proper random numbers
     stream.

Change-Id: I11effdf6f81ca76581a354218203620708195b2b
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/306688
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>

akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics