elf2flt: fix relocations for read-only data

elf2flt: fix relocations for read-only data

Readonly data sections are mapped into the "text" section in the
elf2flt.ld linker script. The relocation generation code is not handling
that case properly though, and is actually mapping any data section type
into the "data" section of the target binary.

This problem case has been detected with elf2flt core dumping when used
with binutils-2.33.1 (on ARM architecture targets). See thread at:

  https://sourceware.org/ml/binutils/2019-10/msg00132.html

Signed-off-by: Greg Ungerer <gerg@kernel.org>