um: stop using PCI port I/O

arch/um is one of the last users of CONFIG_GENERIC_IOMAP, but upon
closer look it appears that the PCI host bridge does not register
any port I/O, and the absense of both custom inb/outb functions and
a PCI_IOBASE constant means that actually trying to use port I/O
results on a NULL pointer access.

Build testing with clang confirms this by warning about this exact
problem:

include/asm-generic/io.h:549:31: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]
  549 |         val = __raw_readb(PCI_IOBASE + addr);
      |                           ~~~~~~~~~~ ^

Remove all the Kconfig selects that refer to legacy port I/O
and instead just build the normal MMIO path that is emulated
by the virtio PCI host.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20250509084125.1488601-1-arnd@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: arndb

arch/um/Kconfig

@@ -52,13 +52,7 @@ config NO_IOMEM
 config UML_IOMEM_EMULATION
 	bool
 	select INDIRECT_IOMEM
-	select HAS_IOPORT
 	select GENERIC_PCI_IOMAP
-	select GENERIC_IOMAP
-	select NO_GENERIC_PCI_IOPORT_MAP
-
-config NO_IOPORT_MAP
-	def_bool !UML_IOMEM_EMULATION
 
 config ISA
 	bool

arch/um/kernel/Makefile

@@ -25,7 +25,6 @@ obj-$(CONFIG_GPROF)	+= gprof_syms.o
 obj-$(CONFIG_OF) += dtb.o
 obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
-obj-$(CONFIG_GENERIC_PCI_IOMAP) += ioport.o
 
 USER_OBJS := config.o