arm: Move bootstage record for board_init_f() to after arch_cpu_init()

The timer may be inited in arch_cpu_init() so it is not safe to make a
bootstage mark before this is called. Arrange the code to fix this.

Note: The question was raised as to why we don't keep all archs in sync.
PowerPC doesn't have specific bootstage markers at present (although it
does use boot progress). I hope that the generic board series will solve
this problem in general, but in the meantime this is a real problem, and
only in ARM.

We now get a correct time for board_init_f:

Timer summary in microseconds:
       Mark    Elapsed  Stage
          0          0  reset
    100,000    100,000  spl_start
    848,530    748,530  board_init_f
    907,301     58,771  board_init_r
    910,478      3,177  board_init

Signed-off-by: Simon Glass <sjg@chromium.org>