efi-loader: when detecting if we are booted in UKI measured boot mode, imply a check...

efi-loader: when detecting if we are booted in UKI measured boot mode, imply a check for TPM2

We simply don't carry any userspace support for TPM1.2 in our tree, and
we shouldn't given it's too weak by today's standards. Hence, if we
check if we are booted in UKI measured boot mode, don't just check if we
are booted in EFI, but also check that we have a TPM2 chip (as opposed
to none or only a TPM1.2 chip).

This is an alternative to #30652 but more comprehensive (and simpler),
since it covers all invocations of efi_measured_uki().

Fixes: #30650
Replaces: #30652