ARM: OMAP4: sleep: build OMAP4 specific functions only for OMAP4

CPU sleep and resume functions for Cortex-A9 based OMAP4 and
Cortex-A15 based OMAP5 are different. Hence, even though we reuse
most of the remaining file as part of OMAP4/5 consolidation, build
OMAP4 specific sleep/resume operations only for OMAP4. SCU is not used
OMAP5.

This fixes the following build failure with OMAP5 only build:
arch/arm/mach-omap2/built-in.o: In function `scu_gp_set':
arch/arm/mach-omap2/sleep44xx.S:132: undefined reference to `scu_power_mode'
arch/arm/mach-omap2/built-in.o: In function `scu_gp_clear':
arch/arm/mach-omap2/sleep44xx.S:229: undefined reference to `scu_power_mode'

Reported-by: Pekon Gupta <pekon@ti.com>
Reported-by: Vincent Stehlé <v-stehle@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>