blackfin, powerpc: remove redundant definitions of ARRAY_SIZE

Since ARRAY_SIZE macro is defined in include/common.h,
re-defining it in arch-specific files is redundant.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Stefan Roese <sr@denx.de>
Acked-by: Sonic Zhang <sonic.zhang@analog.com>