[M] Change in coreboot[master]: util/cbfstool: Add a new mechanism to provide a memory mapped

[Julius Werner (Code Review)]

Attention is currently required from: Nico Huber, Maximilian Brune, Arthur Heymans.

Julius Werner has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/68160 )

Change subject: util/cbfstool: Add a new mechanism to provide a memory mapped
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Patch Set 3:

(4 comments)

File src/soc/intel/common/block/fast_spi/Makefile.inc:

https://review.coreboot.org/c/coreboot/+/68160/comment/fdbebbf7_d934b25b 
PS3, Line 91: $(call int-subtract, $(CONFIG_ROM_SIZE) 0x1000000)
Can we factor this term out into a separate variable (e.g. ext_rom_size or something like that)? I think that would make this easier to read.

File util/cbfstool/cbfstool.c:

https://review.coreboot.org/c/coreboot/+/68160/comment/97cdcc45_f4becb8a 
PS3, Line 317: static int next_window;
nit: namespace a bit better since it's a global (e.g. mmap_next_window)

https://review.coreboot.org/c/coreboot/+/68160/comment/41d6bfd0_c4ee0141 
PS3, Line 338: 	MMAP_SIZE
nit: That's a bit of an odd way to name fields in an array, particularly since these constants are global and not very well namespaced. How about this instead?
```
union {
  unsigned long int array[3];
  struct {
    unsigned long int flash_base;
    unsigned long int mmap_base;
    unsigned long int mmap_size;
  };
} mmap_args;
```

https://review.coreboot.org/c/coreboot/+/68160/comment/8b5af9cb_428c45df 
PS3, Line 358: 			      optarg);
Note that this will no longer print the full argument because strtok() cuts it into pieces in-place. Not sure if we care.