util/cbfstool: Treat region offsets differently than absolute addresses

cbfstool overloads baseaddress to represent multiple things:
1. Address in SPI flash space
2. Address in host space (for x86 platforms)
3. Offset from end of region (accepted as negative number)

This was done so that the different functions that use these
addresses/offsets don't need to be aware of what the value represents
and can use the helper functions convert_to_from* to get the required
values.

Thus, even if the user provides a negative value to represent offset
from end of region, it was stored as an unsigned integer. There are
special checks in convert_to_from_top_aligned which guesses if the
value provided is really an offset from the end of region and converts
it to an offset from start of region.

This has worked okay until now for x86 platforms because there is a
single fixed decode window mapping the SPI flash to host address
space. However, going forward new platforms might need to support more
decode windows that are not contiguous in the host space. Thus, it is
important to distinguish between offsets from end of region and
addresses in host/SPI flash space and treat them separately.

As a first step towards supporting this requirement for multiple
decode windows on new platforms, this change handles the negative
offset provided as input in dispatch_command before the requested cbfs
operation is performed.

This change adds baseaddress_input, headeroffset_input and
cbfsoffset_input to struct param and converts them to offsets from
start of region before storing into baseaddress, headeroffset and
cbfsoffset if the inputs are negative.

In follow up changes, cbfstool will be extended to add support
for multiple decode windows.

BUG=b:171534504
TEST=Verified using abuild with timeless option for all coreboot
boards that there is no change in the resultant coreboot.rom file.

Change-Id: Ib74a7e6ed9e88fbc5489640d73bedac14872953f
Signed-off-by: Furquan Shaikh <furquan@google.com>
---
M util/cbfstool/cbfs_image.c
M util/cbfstool/cbfstool.c
2 files changed, 73 insertions(+), 43 deletions(-)