ARM: davinci: DA850: move da850_register_pm to .init.text

All callers (board-mityomapl138.c and board-da850-evm.c) use it in
__init functions only.

This fixes:

	WARNING: vmlinux.o(.text+0xd664): Section mismatch in reference from the function da850_register_pm() to the function .init.text:da8xx_get_mem_ctlr()
	The function da850_register_pm() references
	the function __init da8xx_get_mem_ctlr().
	This is often because da850_register_pm lacks a __init
	annotation or the annotation of da8xx_get_mem_ctlr is wrong.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>