Minimal iPXE build

[Morian]

Hi !

I needed to build a iPXE EFI loader and everything works quite well so far.
There's an embedded script using the many possibilities of iPXE (thanks for that!).
But this loader is meant to be distributed across a large number of (similar) devices, so I started to look at reducing the generated binary size (starting from ~950KiB)

I found that building secure-boot enabled reduces the size to ~500KiB.
With further features tweaking (through config/local/*.h), I made this a little bit smaller, but it still included a lot of drivers I don't need.
I found no official way to specify a list of drivers, so I started to dig the Makefile a little bit and came with the solution of adding DRIVERS_ipxe=intel on the make invocation (as I only need a specific Intel driver).

Final size is 134KiB and still works as expected.

Do you feel like this technique is safe and future-proof or am I missing something to specify a list of drivers?

Thanks