Optionrom code cleanup.

Optionrom code cleanup.

Nearly all calers of callrom() use OPTION_ROM_INITVECTOR - make it
    default.
Prefer (void*) to explicit casts.
Rename init_optionrom to init_pcirom; rename verifysize_optionrom to
    init_optionrom.
Add 'isvga' parameter to init_optionrom/init_pcirom; unify vga call
    path to use these functions.
Extract cbfs directory scanning into new function run_cbfs_roms().
Allow roms in "vgaroms/" to run even if no pci vga device exists.
Comment improvements.