tpm: Update struct tpm_buf documentation comments

Remove deprecated portions and document enum values.
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

include/linux/tpm.h

@@ -297,15 +297,14 @@ struct tpm_header {
 	};
 } __packed;
 
-/* A string buffer type for constructing TPM commands. This is based on the
- * ideas of string buffer code in security/keys/trusted.h but is heap based
- * in order to keep the stack usage minimal.
- */
-
 enum tpm_buf_flags {
+	/* the capacity exceeded: */
 	TPM_BUF_OVERFLOW	= BIT(0),
 };
 
+/*
+ * A string buffer type for constructing TPM commands.
+ */
 struct tpm_buf {
 	unsigned int flags;
 	u8 *data;