serial: cpm_uart: call cpm_muram_init before registering console

Christophe reports that powerpc 8xx silently fails to 5.6-rc1. It turns
out I was wrong about nobody relying on the lazy initialization of the
cpm/qe muram in commit b6231ea2b3 (soc: fsl: qe: drop broken lazy
call of cpm_muram_init()).

Rather than reinstating the somewhat dubious lazy call (initializing a
currently held spinlock, and implicitly doing a GFP_KERNEL under that
spinlock), make sure that cpm_muram_init() is called early enough - I
thought the calls from the subsys_initcalls were good enough, but when
used by console drivers, that's obviously not the
case. cpm_muram_init() is safe to call twice (there's an early return
if it is already initialized), so keep the call from cpm_init() - in
case SERIAL_CPM_CONSOLE=n.

Fixes: b6231ea2b3 (soc: fsl: qe: drop broken lazy call of cpm_muram_init())
Reported-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>
Link: https://lore.kernel.org/r/20200213114342.21712-1-linux@rasmusvillemoes.dk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/cpm_uart/cpm_uart_core.c

@@ -1373,6 +1373,7 @@ static struct console cpm_scc_uart_console = {
 
 static int __init cpm_uart_console_init(void)
 {
+	cpm_muram_init();
 	register_console(&cpm_scc_uart_console);
 	return 0;
 }