At present CONFIG_SKIP_LOWLEVEL_INIT prevents U-Boot from calling
lowlevel_init(). This means that the instruction cache is not enabled and
the board runs very slowly.

What is really needed in many cases is to skip the call to lowlevel_init()
but still perform CP15 init. Add an option to handle this.
Reviewed-by: NHeiko Schocher <hs@denx.de>
Tested-on: smartweb, corvus, taurus, axm
Tested-by: NHeiko Schocher <hs@denx.de>
Reviewed-by: NJoe Hershberger <joe.hershberger@ni.com>
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NAndreas Bießmann <andreas@biessmann.org>