tpm: End any active auth session before shutdown

Lazy flushing of TPM auth sessions can interact badly with IMA + kexec,
resulting in loaded session handles being leaked across the kexec and
not cleaned up. Fix by ensuring any active auth session is ended before
the TPM is told about the shutdown, matching what is done when
suspending.

Before:

root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
root@debian-qemu-efi:~# systemctl kexec
…
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
- 0x2000000
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#
(repeat kexec steps)
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
- 0x2000000
- 0x2000001
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#

After:

root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
root@debian-qemu-efi:~# systemctl kexec
…
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#

Signed-off-by: Jonathan McDowell <noodles@meta.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>