tsm-mr: Add tsm-mr sample code

This sample kernel module demonstrates how to make MRs accessible to user
mode through the tsm-mr library.

Once loaded, this module registers a `miscdevice` that host a set of
emulated measurement registers as shown in the directory tree below.

/sys/class/misc/tsm_mr_sample
└── measurements
├── config_mr
├── report_digest:sha512
├── rtmr0:sha256
├── rtmr1:sha384
├── rtmr_crypto_agile:sha256
├── rtmr_crypto_agile:sha384
└── static_mr:sha384

Among the MRs in this example:

- `config_mr` demonstrates a hashless MR, like MRCONFIGID in Intel TDX or
HOSTDATA in AMD SEV.
- `static_mr` demonstrates a static MR. The suffix `:sha384` indicates its
value is a sha384 digest.
- `rtmr0` is an RTMR with `TSM_MR_F_WRITABLE` **cleared**, preventing
direct extensions; as a result, the attribute `rtmr0:sha256` is
read-only.
- `rtmr1` is an RTMR with `TSM_MR_F_WRITABLE` **set**, permitting direct
extensions; thus, the attribute `rtmr1:sha384` is writable.
- `rtmr_crypto_agile` demonstrates a "single" MR that supports multiple
hash algorithms. Each supported algorithm has a corresponding digest,
usually referred to as a "bank" in TCG terminology. In this specific
sample, the 2 banks are aliased to `rtmr0` and `rtmr1`, respectively.
- `report_digest` contains the digest of the internal report structure
living in this sample module's memory. It is to demonstrate the use of
the `TSM_MR_F_LIVE` flag. Its value changes each time an RTMR is
extended.

Signed-off-by: Cedric Xing <cedric.xing@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Dionna Amalie Glaze <dionnaglaze@google.com>
Link: https://patch.msgid.link/20250506-tdx-rtmr-v6-2-ac6ff5e9d58a@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>