ARM: OMAP5+: Reuse OMAP4 PM code for OMAP5 and DRA7

OMAP4, OMAP5 and DRA7 share a lot of common logic and data structures.
These have been enabled in the previous patches, however, this also
means that OMAP5 or DRA7 only builds also need to build OMAP4 logic.
Update to reuse OMAP4 logic.

This fixes the 'undefined reference to 'omap4_pm_init_early'' in
OMAP5 or DRA7 only builds.

Fixes: 6af16a1d ("ARM: DRA7: Add hook in SoC initcalls to enable pm initialization")
Fixes: 628ed471 ("ARM: OMAP5: Add hook in SoC initcalls to enable pm initialization")
Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>