commands/ieee1275/ibmvtpm: Add support for trusted boot using a vTPM 2.0

Add support for trusted boot using a vTPM 2.0 on the IBM IEEE1275
PowerPC platform. With this patch grub now measures text and binary data
into the TPM's PCRs 8 and 9 in the same way as the x86_64 platform
does.

This patch requires Daniel Axtens's patches for claiming more memory.

Note: The tpm_init() function cannot be called from GRUB_MOD_INIT() since
it does not find the device nodes upon module initialization and
therefore the call to tpm_init() must be deferred to grub_tpm_measure().

For vTPM support to work on PowerVM, system driver levels 1010.30
or 1020.00 are required.

Note: Previous versions of firmware levels with the 2hash-ext-log
API call have a bug that, once this API call is invoked, has the
effect of disabling the vTPM driver under Linux causing an error
message to be displayed in the Linux kernel log. Those users will
have to update their machines to the firmware levels mentioned
above.

Cc: Eric Snowberg <eric.snowberg@oracle.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Reviewed-by: Robbie Harwood <rharwood@redhat.com>

docs/grub.texi

@@ -6525,7 +6525,8 @@ tpm module is loaded. As such it is recommended that the tpm module be built
 into @file{core.img} in order to avoid a potential gap in measurement between
 @file{core.img} being loaded and the tpm module being loaded.
 
-Measured boot is currently only supported on EFI platforms.
+Measured boot is currently only supported on EFI and IBM IEEE1275 PowerPC
+platforms.
 
 @node Lockdown
 @section Lockdown when booting on a secure setup