ide: pass number of ports to ide_host_{alloc,add}() (v2)

Pass number of ports to ide_host_{alloc,add}() and then update
all users accordingly.

v2:
- drop no longer needed NULL initializers in buddha.c, cmd640.c and gayle.c
  (noticed by Sergei)

There should be no functional changes caused by this patch.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>