KEYS: trusted: Debugging as a feature

TPM_DEBUG, and other similar flags, are a non-standard way to specify a
feature in Linux kernel. Introduce CONFIG_TRUSTED_KEYS_DEBUG for trusted
keys, and use it to replace these ad-hoc feature flags.

Given that trusted keys debug dumps can contain sensitive data, harden the
feature as follows:

1. In the Kconfig description postulate that pr_debug() statements must be
   used.
2. Use pr_debug() statements in TPM 1.x driver to print the protocol dump.
3. Require trusted.debug=1 on the kernel command line (default: 0) to
   activate dumps at runtime, even when CONFIG_TRUSTED_KEYS_DEBUG=y.

Traces, when actually needed, can be easily enabled by providing
trusted.dyndbg='+p' and trusted.debug=1 in the kernel command-line.

Reported-by: Nayna Jain <nayna@linux.ibm.com>
Closes: https://lore.kernel.org/all/7f8b8478-5cd8-4d97-bfd0-341fd5cf10f9@linux.ibm.com/
Reviewed-by: Nayna Jain <nayna@linux.ibm.com>
Tested-by: Srish Srinivasan <ssrish@linux.ibm.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>