ARM: OMAP4+: hwmod: Add hwmod flag for HWMOD_OMAP4_ZERO_CLKCTRL_OFFSET

Nearly all modules on OMAP4 and newer platforms have clkctrl offsets
that are non-zero except for the RTC on am335x. Because we rely on a
clkctrl_offset of zero to indicate no clkctrl_offset being present,
lets add a HWMOD_OMAP4_ZERO_CLKCTRL_OFFSET flag to use to indicate
hwmods that have a valid clkctrl_offset of 0.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>