topology: improve the printf buffer management

topology: improve the printf buffer management

The commit d04e72c9a593015952e4858b92ab3f9d821560d9 introduced
the dynamic printf buffer allocation for each tplg_save_printf()
call.

Introduce 'struct tplg_buf' which carries extra information about
the temporary printf buffer and the destination buffer to save allocation
requests.

The printf buffer is also allocated using 1024 bytes chunks.

A comparison between 'alloc everyting' and 'cache+chunk alloc' for the
random picked topology file:

  1: 18,620 allocs, 18,620 frees, 7,239,688 bytes allocated
  2: 12,490 allocs, 12,490 frees, 962,568 bytes allocated

Signed-off-by: Jaroslav Kysela <perex@perex.cz>