package/elf2flt: fix text relocations on xtensa

elf2flt 2021.08 has changed endianness swapping logic for relocated
entries in the text segment. This broke little-endian xtensa FLAT images
which now fail to start with the following message:

  binfmt_flat: reloc outside program 0x24c80100 (0 - 0x6e430/0x56a20)

Fix it by restoring old endianness swapping logic for relocated entries
in the text segment when building for xtensa.

Reported-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>