serial: cpm_uart: Fix a COMPILE_TEST dependency

In a COMPILE_TEST configuration, the cpm_uart driver uses symbols from
the cpm_uart_cpm2.c file. This file is compiled only when CONFIG_CPM2 is
set.

Without this dependency, the linker fails with some missing symbols for
COMPILE_TEST configuration that needs SERIAL_CPM without enabling CPM2.

This lead to:
  depends on CPM2 || CPM1 || (PPC32 && CPM2 && COMPILE_TEST)

This dependency does not make sense anymore and can be simplified
removing all the COMPILE_TEST part.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202305160221.9XgweObz-lkp@intel.com/
Fixes: e3e7b13b ("serial: allow COMPILE_TEST for some drivers")
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/20230523085902.75837-3-herve.codina@bootlin.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>