tpm: Implement tpm_sized_buffer_reset

Move the definition of TPMSizedBuffer out of tpm_tis.c into tpm_util.h
and implement tpm_sized_buffer_reset() for the following patches to use.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

hw/tpm/tpm_tis.c

@@ -48,11 +48,6 @@ typedef enum {
     TPM_TIS_STATE_RECEPTION,
 } TPMTISState;
 
-typedef struct TPMSizedBuffer {
-    uint32_t size;
-    uint8_t  *buffer;
-} TPMSizedBuffer;
-
 /* locality data  -- all fields are persisted */
 typedef struct TPMLocality {
     TPMTISState state;

hw/tpm/tpm_util.c

@@ -355,3 +355,10 @@ int tpm_util_get_buffer_size(int tpm_fd, TPMVersion tpm_version,
 
     return 0;
 }
+
+void tpm_sized_buffer_reset(TPMSizedBuffer *tsb)
+{
+    g_free(tsb->buffer);
+    tsb->buffer = NULL;
+    tsb->size = 0;
+}

hw/tpm/tpm_util.h

@@ -42,4 +42,11 @@ int tpm_util_get_buffer_size(int tpm_fd, TPMVersion tpm_version,
 #define DEFINE_PROP_TPMBE(_n, _s, _f)                     \
     DEFINE_PROP(_n, _s, _f, qdev_prop_tpm, TPMBackend *)
 
+typedef struct TPMSizedBuffer {
+    uint32_t size;
+    uint8_t  *buffer;
+} TPMSizedBuffer;
+
+void tpm_sized_buffer_reset(TPMSizedBuffer *tsb);
+
 #endif /* TPM_TPM_UTIL_H */