sh: bios: Revive earlyprintk support

The SuperH BIOS earlyprintk code is protected by CONFIG_EARLY_PRINTK.
However, when this protection was added, it was missed that SuperH no
longer defines an EARLY_PRINTK config symbol since commit
e76fe57 ("sh: Remove old early serial console code V2"), so
BIOS earlyprintk can no longer be used.

Fix this by reviving the EARLY_PRINTK config symbol.

Fixes: d0380e6 ("early_printk: consolidate random copies of identical code")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/c40972dfec3dcc6719808d5df388857360262878.1697708489.git.geert+renesas@glider.be
Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>

arch/sh/Kconfig.debug

@@ -22,6 +22,17 @@ config STACK_DEBUG
 	  every function call and will therefore incur a major
 	  performance hit. Most users should say N.
 
+config EARLY_PRINTK
+	bool "Early printk"
+	depends on SH_STANDARD_BIOS
+	help
+	  Say Y here to redirect kernel printk messages to the serial port
+	  used by the SH-IPL bootloader, starting very early in the boot
+	  process and ending when the kernel's serial console is initialised.
+	  This option is only useful while porting the kernel to a new machine,
+	  when the kernel may crash or hang before the serial console is
+	  initialised.  If unsure, say N.
+
 config 4KSTACKS
 	bool "Use 4Kb for kernel stacks instead of 8Kb"
 	depends on DEBUG_KERNEL && (MMU || BROKEN) && !PAGE_SIZE_64KB