ARM: OMAP: AM3517/3505: fix crash on boot due to incorrect voltagedomain data

AM3517/3505 chips don't have voltage controller and voltage processor
IP blocks.  Trying to use OMAP34xx/36xx voltage domain data on these
chips causes a crash during boot:

  omap_vc_init_channel: PMIC info requried to configure vc forvdd_core not populated.Hence cannot initialize vc
  Unable to handle kernel NULL pointer dereference at virtual address 00000025
  pgd = c0004000
  [00000025] *pgd=00000000
  Internal error: Oops: 5 [#1] SMP
  Modules linked in:
  CPU: 0    Tainted: G        W     (3.2.0-rc5-00006-g402ecf4 #304)
  PC is at omap_vp_init+0x5c/0x14c
  LR is at omap_vp_init+0x54/0x14c

Fix this by using very minimal voltage domain definitions for AM3517/3505.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Kevin Hilman <khilman@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>