target: Allocate aptpl_buf inside update_and_write_aptpl()

Instead of taking the buffer and length, update_and_write_aptpl() will
allocate the buffer as needed, and then free it. Instead, the function
takes an 'aptpl' boolean parameter.

This enables us to remove memory alloc/frees from struct
t10_pr_registration and other spots.

There is a slight loss of functionality because each callsite doesn't get
its own pr_debug any more, but this info can be cleaned via ftrace if
necessary and I think the shorter code is worth it.
Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

include/target/target_core_base.h

@@ -339,8 +339,6 @@ struct t10_pr_registration {
 	/* Used during APTPL metadata reading */
 #define PR_APTPL_MAX_TPORT_LEN			256
 	unsigned char pr_tport[PR_APTPL_MAX_TPORT_LEN];
-	/* For writing out live meta data */
-	unsigned char *pr_aptpl_buf;
 	u16 pr_aptpl_rpti;
 	u16 pr_reg_tpgt;
 	/* Reservation effects all target ports */