arm, arm926ejs: Do cpu critical inits only for boards that require it

This patch reverts commit ca4b5580
"arm, arm926ejs: always do cpu critical inits" since it impacts all
arm926ejs based configurations and caused problems, e.g., with
the hawkboard.

Instead the patch removes the CONFIG_SKIP_LOWLEVEL_INIT defines
from the board configurations that need low level initialization.

Signed-off-by: Christian Riesch <christian.riesch@omicron.at>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Tom Rini <trini@ti.com>
Cc: Heiko Schocher <hs@denx.de>
Acked-by: Heiko Schocher <hs@denx.de>
Tested-by: Heiko Schocher <hs@denx.de>