sh: dreamcast: Fix GAPS PCI bridge addressing

The G2-to-PCI bridge chip found in SEGA Dreamcast assumes P2 area
relative addresses.

Set the appropriate IOPORT base offset.
Tested-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Artur Rojek <contact@artur-rojek.eu>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/20240511191614.68561-2-contact@artur-rojek.euSigned-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>

arch/sh/Kconfig

@@ -125,7 +125,8 @@ config ARCH_HAS_ILOG2_U64
 
 config NO_IOPORT_MAP
 	def_bool !PCI
-	depends on !SH_SHMIN && !SH_HP6XX && !SH_SOLUTION_ENGINE
+	depends on !SH_SHMIN && !SH_HP6XX && !SH_SOLUTION_ENGINE && \
+		   !SH_DREAMCAST
 
 config IO_TRAPPED
 	bool

arch/sh/boards/mach-dreamcast/setup.c

@@ -25,10 +25,13 @@
 #include <asm/irq.h>
 #include <asm/rtc.h>
 #include <asm/machvec.h>
+#include <cpu/addrspace.h>
 #include <mach/sysasic.h>
 
 static void __init dreamcast_setup(char **cmdline_p)
 {
+	/* GAPS PCI bridge assumes P2 area relative addresses. */
+	__set_io_port_base(P2SEG);
 }
 
 static struct sh_machine_vector mv_dreamcast __initmv = {