TPM code fixes - #8305

The swtpm control socket is a Unix SOCK_STREAM, so a single read() is
not guaranteed to return the full response in one shot. swtpm may
split a response into multiple writes, in which case the existing
single read() returns only the first chunk and subsequent parsing
fails with "Response for ... cmd is of incorrect length". This has
been observed on Azure Linux during emulator initialization.

In addition, when swtpm encounters an error processing a control
command (e.g. PTM_BAD_ORDINAL = 0x0A returned for commands issued
before CMD_INIT), the swtpm protocol returns only the 4-byte result
code instead of the full response. Blindly looping until msg_len_out
bytes arrive would deadlock in that case.

Add SocketDev::read_exact() that loops until the requested number of
bytes has been received (retrying on EINTR), and rework
run_control_cmd() to:

  * read_exact the 4-byte result code first;
  * on error, set the result code on the PTM message and return a
    clean error without waiting for a payload that will never arrive;
  * on success, read_exact the remaining (msg_len_out - 4) payload
    bytes.

Assisted-by: Copilot:GPT-5.5
Signed-off-by: Wei Liu <[email protected]>

The helper used to communicate the TPM Establishment bit between the
swtpm backend and the CRB device had inverted semantics:

    self.established_flag = est.resp.bit == 0;

so `established_flag == true` actually meant "*not* established". The
device-side call site then double-negated:

    if !self.emulator.get_established_flag() {
        val |= 0x1;  // tpmEstablished in TPM_LOC_STATE
    }

The end-to-end behaviour was correct but the boundary between the
swtpm-specific backend and the (TCG-spec defined) CRB device was hard
to follow and easy to misuse -- the now-removed pre-init check in
Emulator::new() was an example of that confusion (it errored out with
"TPM not in established state" precisely when the TPM *was*
established).

Per the TCG PC Client Platform TPM Profile (PTP) specification, bit 0
of TPM_LOC_STATE_x is `tpmEstablished`:

  * 0 = default state after a cold reset
  * 1 = a TPM2_Startup from Locality 3 or 4 has occurred

Rename the backend accessor to `get_established_bit()` and return the
bit value directly (true == 1, false == 0). The CRB device then simply
forwards the bit, with no inversion, which makes the spec mapping
obvious and removes swtpm-flavoured naming from the device layer.

No functional change.

Asissted-by: Copilot:GPT-5.5
Signed-off-by: Wei Liu <[email protected]>