x86: remove arbitrary ELF section limit in i386 relocatable kernel

Impact: build failure in maximal configurations

The 32-bit x86 relocatable kernel requires an auxilliary host program
to process the relocations.  This program had a hard-coded arbitrary
limit of a 100 ELF sections.  Instead of a hard-coded limit, allocate
the structures dynamically.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>