efi/libstub: x86/mixed: increase supported argument count

efi/libstub: x86/mixed: increase supported argument count

Increase the number of arguments supported by mixed mode calls, so that
we will be able to call into the TCG2 protocol to measure the initrd
and extend the associated PCR. This involves the TCG2 protocol's
hash_log_extend_event() method, which takes five arguments, three of
which are u64 and need to be split, producing a total of 8 outgoing

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Link: https://lore.kernel.org/r/20211119114745.1560453-3-ilias.apalodimas@linaro.org
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>