vtpm: Upgrade to using tpm_emulator-0.5.1

vtpm: Upgrade to using tpm_emulator-0.5.1

The newer version of the emulator contains several bug fixes, one that
we were seeing in our use of vtpm.

This patch also defines TPM_STRONG_PERSISTENCE for the new emulator.

A couple of important notes about this patch:
-This has only been tested on PVM domU's. In theory it should work for
HVM but I have not tried it at all and can guarantee nothing.
-All the relevant changes in tools/vtpm/vtpm.patch have been ported
to tpm_emulator-0.5.1.
-None of the changes in tpm_emulator.patch have been ported. In
particular this means the BUILD_EMULATOR option, which as I understand
lets you use the tpm_emulator in dom0 for a machine that does
not have a real hardware TPM does not work. This functionality should
be easy to add though because the new emulator already comes with a
kernel module interface.
-No considerations were made for the VTPM_MULTI_VM feature (which is
supposedly unfinished). This patch may or may not break any progress
made on that feature.

Signed-off-by: Matt Fioravante <Matthew.Fioravante@jhuapl.edu>