xtensa: fix endianness
xtensa: fix endianness

machdata["elf"] has endianness encoded into it, and it doesn't match
endianness in archinfo['xtensa']. Fix machdata["elf"] definition to be
little endian.

Normally endianness in machdata["elf"] and in archinfo['xtensa'] should
be toolchain build parameters.

Change-Id: Ia4c746a923c2fbdd4e447c13d0b33d95cef498d1
Signed-off-by: Max Filippov <8c5ea195856807f4f02a6e0749c87ea6b7375f38@gmail.com>

zephyrproject-rtos/meta-zephyr-sdk,zephyrproject-rtos/meta-zephyr-sdk,zephyrproject-rtos/meta-zephyr-sdk,zephyrproject-rtos/meta-zephyr-sdk