OMAP2+: Fix random config build break with !ARM_CPU_SUSPEND

The random config builds with PM and !ARM_CPU_SUSPEND breaks with below
error on omap2plus_defconfig.

arch/arm/mach-omap2/sleep44xx.S:323: undefined reference to `cpu_resume'
arch/arm/mach-omap2/omap-mpuss-lowpower.c:278: undefined reference to `cpu_suspend'

This is because recently merged OMAP5 platform shares the common files
with OMAP4 but doesn't select ARM_CPU_SUSPEND. Without the ARM_CPU_SUSPEND
the sleep code is meaningless.

Fix the same by adding ARM_CPU_SUSPEND for OMAP5. The suggestion came from
Russell King in an off-list discussion.

Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Kevin Hilman <khilman@ti.com>
Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>