Don't waste tracepoint segment memory on per-btree block allocation
tracepoints when we can do it from the generic btree code.

With this patch applied, two tracepoints are collapsed into one
tracepoint, with the following effects on objdump -hx xfs.ko output:

Before:

 10 __tracepoints_ptrs 00000b38  0000000000000000  0000000000000000  001412f0  2**2
 14 __tracepoints_strings 00005433  0000000000000000  0000000000000000  001689a0  2**5
 29 __tracepoints 00010d30  0000000000000000  0000000000000000  0023fe00  2**5

After:

 10 __tracepoints_ptrs 00000b34  0000000000000000  0000000000000000  001417b0  2**2
 14 __tracepoints_strings 00005413  0000000000000000  0000000000000000  00168e80  2**5
 29 __tracepoints 00010cd0  0000000000000000  0000000000000000  00240760  2**5

Column 3 is the section size in bytes; removing these two tracepoints
reduces the size of the ELF segments by 132 bytes.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>