[Blackfin] arch: fix bug kernel boot message: memory information is not reasonable

Some of the information in kernel boot message is not reasonable.
http://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_item_id=3846

 - use _rambase as the start of kernel image.
   kernel is in the region [_rambase, _ramstart]
 - count in pages in per-cpu-page list as available memory
 - reserved memory now include: [0 - 4K] for bad pointer catching,
   memory reserved for abnormaly 05000263, memory reserved by kernel itself.

Signed-off-by: Yi Li <yi.li@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>

arch/blackfin/kernel/setup.c

@@ -238,6 +238,7 @@ void __init setup_arch(char **cmdline_p)
 	memory_end = _ramend - DMA_UNCACHED_REGION;
 
 	_ramstart = (unsigned long)__bss_stop;
+	_rambase = (unsigned long)_stext;
 #ifdef CONFIG_MPU
 	/* Round up to multiple of 4MB.  */
 	memory_start = (_ramstart + 0x3fffff) & ~0x3fffff;