build: Simplify detecting a TPM emulator.
* configure.ac (TPMSERVER): Don't supply hard-coded path. (SWTPM, SWTPM_IOCTL, TSSSTARTUP): Likewise.
Cherry-picked from master commit of:
f2ca727978da5b1ed84f97bf37d604e8a4e60091
Having hard-coded path has bad side effect; It may not be detected
even if it's available with PATH.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>