ARM: OMAP2+: PRM: determine PRM base address from device tree

There is no need to provide the PRM base address through a low-level API
from the low-level IO init, as this information is available through DT.
Re-routed the parsing function to be called from the PRM drivers also to
simplify the implementation under io.c.

Signed-off-by: Tero Kristo <t-kristo@ti.com>

arch/arm/mach-omap2/prm.h

@@ -20,6 +20,7 @@ extern void __iomem *prm_base;
 extern u16 prm_features;
 extern void omap2_set_globals_prm(void __iomem *prm);
 int omap_prcm_init(void);
+int omap2_prm_base_init(void);
 void omap3_prcm_legacy_iomaps_init(void);
 # endif