scripts/nuttx2ffff: fix generated output files
scripts/nuttx2ffff: fix generated output files

The current files output by this script have some issues:

- Unnecessary .tftf files are left in the output directory

- .ffff files are generated for ES2, a target for which they are not
  useful

- nuttx defconfig names are hard-coded inside, adding an unnecessary
  dependency that is prone to breakage since those defconfig names
  change

- Both APB and GPB builds are always generated, when in some
  cases (e.g. the APBA defconfig) only the APB target build is needed

To fix these:

- Delete the "build" option, which took a nuttx defconfig

- Replace it with a mandatory --target option, to specify one of instead
  of generating both APB and GPB versions

- Only generate a single .ffff in the output directory, and just for the
  one target (AP or GP bridge) specified by the caller. Make the name of
  this file match the input ELF file basename + {apb,gpb} + .ffff.

- Don't leave intermediate tftf files behind in the output directory

Testing Done: confirm only one .ffff generated; verify MID/PID of ffff
              using display-ffff
Bug Number: SW-2744
Review URL: https://reviews.leaflabs.com/r/2748/
Reviewed by: Eli Sennesh, Mark Greer

Signed-off-by: Marti Bolivar <35e491f5b70a779e5455b1f9617e0073292369ca@leaflabs.com>

projectara/bootrom-tools,gregkh/bootrom-tools,gregkh/bootrom-tools,gregkh/bootrom-tools,projectara/bootrom-tools,projectara/bootrom-tools