ARM: OMAP4+: PM: erratum is used by OMAP5 and DRA7 as well

OMAP5 and DRA7 reuse the same pm44xx_erratum variable so, enable the
same, else PM features such as Suspend to ram is broken in a SoC only
build configuration.

Reported-by: Carlos Hernandez <ceh@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>