DSS: Implement workaround for Errata ID:i733.

Description of Errata i733:
Due to wrong timings, all register accesses transitioning through the L4
interconnect toward DSS are not reliable.

Workaround:
DSS register access should be addressed through the L3 interconnect.

This change fixes errata by using L3 for access to DSS in dss_hwmod
instead of L4.

Silicon Versions Impacted:
OMAP4430 ES1.0, ES2.0, ES2.1, ES2.2, ES2.3
OMAP4460 ES1.0, ES1.1
OMAP4470 ES1.0