The old startup process consisted of several CFG_LOWBOOT,
CFG_RAMBOOT ifdeffery which I do not understand. So remove
all this and replace it with:

- put the entry point for second stage loaders to offset 0x0
  so that we can do a go /dev/ram0 to start a second barebox
- When we come from the reset vector assume MBAR is at 0x80000000
- When we come from the second stage entry assume that
  SPR 311 is in sync with the current MBAR address.
- Switch MBAR to 0xf0000000 and we are done.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>