tpm: move tpm_getcap to tpm1-cmd.c

1. Move tpm_getcap to tpm1-cmd. Rename the function to tpm1_getcap.
2. Remove unused tpm_getcap_header with unused constant
as this functionality is already implemented using tpm_buf construct.

Fixes warning:
drivers/char/tpm/tpm-interface.c:452:38: warning: ‘tpm_getcap_header’ defined but not used [-Wunused-const-variable=]
 static const struct tpm_input_header tpm_getcap_header = {
                                      ^~~~~~~~~~~~~~~~~
3. Drop unused TPM_DIGEST_SIZE. It's already defined in
include/linux/tpm.h

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>