activate serial console in grub/UEFI, change baud rate to 115200

Before this patch a serial console was only enabled in syslinux for
traditional BIOS, not in grub / UEFI. In traditional BIOS the baud rate
was 38400 before.

Today 38400 is rarely used anymore and most modern devices using a
serial console default to 115200, which is the highest baudrate possible
with the original UART-ICs. Modern UART-ICs usually support higher
baudrates too, but they need a special driver for that. So 115200
is often used because of the wider compatibility.

In grub and syslinux a serial console can fully work in parallel to the
regular console. So enabling it doesn't change anything when nothing is
connected to the serial console or no serial port is installed at all.

This commit only touches the bootloaders, not the boot entries.

efiboot/grub/grubsrcd.cfg

@@ -20,6 +20,12 @@ if loadfont /boot/grub/font.pf2 ; then
 	terminal_output gfxterm
 fi
 
+# enable serial console with common settings (ttyS0, 115200 Baud, 8n1)
+# this works in parallel to regular console
+serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
+terminal_input --append serial
+terminal_output --append serial
+
 menuentry "Boot SystemRescue using default options" {
 	set gfxpayload=keep
 	linux /%INSTALL_DIR%/boot/%ISO_ARCH%/vmlinuz archisobasedir=%INSTALL_DIR% archisolabel=%ARCHISO_LABEL% %DEFAULT_KERNEL_PARAM%

syslinux/sysresccd_head.cfg

@@ -1,4 +1,4 @@
-SERIAL 0 38400
+SERIAL 0 115200
 UI boot/syslinux/vesamenu.c32
 MENU TITLE SYSTEM-RESCUE %ISO_VERSION% %ISO_ARCH% (www.system-rescue.org)
 MENU BACKGROUND #c000a8a8