OMAP2+: hwmod: add API to handle autoidle mode

Create a new API that forms a wrapper to _set_module_autoidle()
to modify the AUTOIDLE bit.

This API is intended to be used by drivers that requires direct
manipulation of the AUTOIDLE bits in SYSCONFIG register.
McBSP driver requires autoidle bit to be enabled/disabled while
using sidetone feature.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Benoit Cousson <b-cousson@ti.com>
[paul@pwsan.com: restrict the hwmod states that the autoidle bit can be changed
 in; changed function name; dropped "int" from "unsigned int long"]
Signed-off-by: Paul Walmsley <paul@pwsan.com>