ARM: OMAP2: hwmod_data: Remove legacy mailbox data and addrs

OMAP2 devices are devicetree boot only, and the legacy mode
of mailbox device creation should no longer be used, so remove
the mailbox attribute data and the hwmod addr space used for
creating mailboxes in legacy mode.

Acked-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>