efi/x86: Drop redundant .bss section

In commit

  c7fb93ec

 ("x86/efi: Include a .bss section within the PE/COFF headers")

we added a separate .bss section to the PE/COFF header of the compressed
kernel describing the static memory footprint of the decompressor, to
ensure that it has enough headroom to decompress itself.

We can achieve the exact same result by increasing the virtual size of
the .text section, without changing the raw size, which, as per the
PE/COFF specification, requires the loader to zero initialize the delta.

Doing so frees up a slot in the section table, which we will use later
to describe the mixed mode entrypoint.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>