kernelarch-mips/config.{4,5}kc-malta are exact duplicates of each other,
aside from the CPU type. Move all the common options out into
kernelarch-mips/config.malta.
Move mips/config.{4,5}kc-malta to kernelarch-mips where they belong,
adding '-r1' and '-r2' suffixes for the different CPU types.
- Enable it by default
- Disable it for armel/marvell since signature verification is not enabled.
- Disable it for mips and mipsel so linux-signed can be uploaded without
waiting for them to build
- Disable it for all architectures not in the main archive, as linux-signed
won't support them (at least, not initially).
We don't need a variable to control signing of the image, because
we should do that for all flavours that have CONFIG_EFI_STUB=y.