gayle: reserve memory resources at once

* Reserve memory resources for all IDE ports at once by moving
  request_mem_region() out of 'for ()' loop and always defining
  GAYLE_IDEREG_SIZE to 0x2000.

* Keep memory resources even if no free IDE slots can be found
  (this driver is unloadable currently).

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>