hvm: TCGBIOS fixes

hvm: TCGBIOS fixes

Fix IPL measurement of El Torito CD boot and some eventlog formats.

The TCG BIOS extensions are described here:
https://www.trustedcomputinggroup.org/specs/PCClient/TCG_PCClientImplementationforBIOS_1-20_1-00.pdf

- fix cdrom (El Torito) boot (8.2.5.6 El Torito, p63)
   tcpa_ipl() is modified to support various boot devices.
   move some measurement code into cdrom_boot() function.
- fix EV_IPL (0Dh) event (10.4.1 Event Types, p76)
   eventfield size should be zero
- fix EV_SEPARATOR event (3.2.2 Integrity Collection and Reporting,
   p32)
   change eventfield to -1 (0xFFFFFFFF)  from  "---------------"
- add "Returned INT 19h" event (8.2.3 Logging of Boot Events, p59)
   actually, tcgbios does not call int19h, but we extend this
   tentatively

Signed-off-by: Seiji Munetoh <seiji.munetoh@gmail.com>