tty: serial: make SERIAL_SPRD not depend on ARCH_SPRD

Remove the dependency with ARCH_SPRD from sprd serial/console Kconfig-s,
since we want them can be built-in when ARCH_SPRD is set as 'm'.

Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lore.kernel.org/r/20200305103228.9686-2-zhang.lyra@gmail.com


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