x86: Convert board_init_f_r to a processing loop

Create an init function array for board_init_f_r - This finalises the
migration to a purely array based initialisation mechanism

Also tweak a few comments while we are at it so everything is 'correct'

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Changes for v2:
 - Renamed to a more apt name
 - Fix bug in set_reloc_flag_r
 - Re-instate gd->flags = boot_flags; in board_init_f
 - Added commit message