serial: cpm_uart: Remove cpm_uart/ subdirectory

cpm_uart/ subdirectory only has cpm_uart_core.c and cpm_uart.h now.

Move them up and remove cpm_uart/ directory while renaming
cpm_uart_core.c as cpm_uart.c

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/9b8b8f89fc386480030f5339abe307541ae436a6.1691068700.git.christophe.leroy@csgroup.eu


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