[sw/silicon_creator] Read boot data in mask_rom_init()
[sw/silicon_creator] Read boot data in mask_rom_init()

This change adds an in memory copy of the boot data read from flash.
This copy is checked in `mask_rom_boot()` before the execution is handed
over to ROM_EXT.

Signed-off-by: Alphan Ulusoy <23b245cc5a07aacf75a9db847b24c67dee1707bf@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan