powerpc: move iSeries_setup.[ch] and mf.c into platforms/iseries

iSeries_setup.c becomes setup.c
iSeries_setup.h becomes setup.h
mf.c retains its name

Also moved iSeries_[gs]et_rtc_time and iSeries_get_boot_time into
mf.c since they are just small wrappers around mf_ functions.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>