AM3517 inherits OMAP3 dts file, but does not have all the IPs
that are present on OMAP3. This patch disables the following
absent IPs for AM3517: Mailbox, IVA, MMU_ISP, MPU_IVA SmartReflex.

A label had to be added for IVA node in omap3.dtsi to be able to
get a reference to the node for disabling.

Otherwise we get the following warnings during booting:
platform iva.2: Cannot lookup hwmod 'iva'
platform 48094000.mailbox: Cannot lookup hwmod 'mailbox'
platform 480bd400.mmu: Cannot lookup hwmod 'mmu_isp'
platform 480c9000.smartreflex: Cannot lookup hwmod 'smartreflex_mpu_iva'
Signed-off-by: Suman Anna <s-anna@ti.com>
[tony@atomide.com: updated description for the warnings]
Signed-off-by: Tony Lindgren <tony@atomide.com>