src/arch/xtensa/CMakeLists.txt: drop bogus, non-portable -Wl,-EL

As already discussed in commit bcbcec7 ("cmake: drop
binutils-specific '-Wl,-EL' option") and commit ee58fef
("smex/cmake: move -Wl,EL option to target_linker_options() for clang")
and their corresponding reviews on GitHub, this binutils-specific,
endianness option makes no difference and is causing clang compatibility
issues. It's now getting in the way of thesofproject#9351 "Add the new platform
ACP_7_0".

I ran `./scripts/docker-run.sh ./scripts/xtensa-build-all.sh -a` with
and without it and there was absolutely zero binary difference.

I was added in 2019 by giant commit e0ba98d ("cmake: add CMakeLists
for firmware build") without any rationale of why it would be needed.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

src/arch/xtensa/CMakeLists.txt

@@ -123,7 +123,6 @@ target_compile_options(sof_options INTERFACE
  $<$<COMPILE_LANGUAGE:C>:
  -${optimization_flag} -g
  -Wall -Werror
- -Wl,-EL
  -Wmissing-prototypes
  -Wpointer-arith
  ${XTENSA_C_FLAGS}