[HVM] Add TCG BIOS extensions to the high memory area along with

[HVM] Add TCG BIOS extensions to the high memory area along with
some often-used libc utility functions. The TCG extensions are
described here:

https://www.trustedcomputinggroup.org/specs/PCClient/TCG_PCClientImplementationforBIOS_1-20_1-00.pdf

I have tried to keep the patching with rombios.c to a minimum, but
some amount of code needs to be inserted at various locations.

The code is currently deactivated, but can be activated by setting
BX_TCGBIOS to '1'.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>