ARM: OMAP: AM35x: remove hwmods that aren't generic

Removing modules iva, sr1_hwmod, sr2_hwmod, mailbox from
the base omap3xxx_hwmods list, so that they can be excluded
for am35x.  This removes quite a few warnings on boot for AM35x.

Signed-off-by: Abhilash K V <abhilash.kv@ti.com>
[paul@pwsan.com: dropped 'mailbox class' comments; updated changelog]
Signed-off-by: Paul Walmsley <paul@pwsan.com>