ARM: OMAP4: Fix definition of IS_PM44XX_ERRATUM

ARM: OMAP4: Fix definition of IS_PM44XX_ERRATUM

Just like IS_PM34XX_ERRATUM, IS_PM44XX_ERRATUM is valid only if
CONFIG_PM is enabled, else, disabling CONFIG_PM results in build
failure complaining about the following:
arch/arm/mach-omap2/built-in.o: In function `omap4_boot_secondary':
:(.text+0x8a70): undefined reference to `pm44xx_errata'

Fixes: e4a578c (ARM: OMAP4: PM: add errata support)
Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.ocm>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>