flashrom.c: Add helper functions for new erase selction algorithm

1) Add function to flatten out the addresses of the flash chip as per
the different erase functions. This function will return a list of
layouts which is dynamically allocated. So after use all the layouts as
well as the list itself should be freed. The free_erase_layout function
does that.

2) Add function to align start and end address of the region (in struct
walk_info) to some erase sector boundaries and modify the region start
and end addresses to match nearest erase sector boundaries. This
function will be used in the new algorithm for erase function selection.

3) Add function that returns a list of sectors (as seen by the first
erase function) that need erasing.

Change-Id: Ic57ca1cca3d1646543f6b5939ba9c35db8d08256
Signed-off-by: Aarya Chaumal <aarya.chaumal@gmail.com>
---
A erasure_layout.c
A erasure_layout.h
2 files changed, 286 insertions(+), 0 deletions(-)