cdx: don't select CONFIG_GENERIC_MSI_IRQ

cdx: don't select CONFIG_GENERIC_MSI_IRQ

x86 does not use CONFIG_GENERIC_MSI_IRQ, and trying to enable it anyway
results in a build failure:

In file included from include/linux/ssb/ssb.h:10,
                 from drivers/ssb/pcihost_wrapper.c:18:
include/linux/gpio/driver.h:41:33: error: field 'msiinfo' has incomplete type
   41 |         msi_alloc_info_t        msiinfo;
      |                                 ^~~~~~~
In file included from include/linux/kvm_host.h:19,
                 from arch/x86/events/intel/core.c:17:
include/linux/msi.h:528:33: error: field 'alloc_info' has incomplete type
  528 |         msi_alloc_info_t        alloc_info;

Change the driver to actually build without this symbol and remove the
incorrect 'select' statements.

Fixes: e8b18c11731d ("cdx: Fix missing GENERIC_MSI_IRQ on compile test")
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
Signed-off-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
Link: https://lore.kernel.org/r/20250826043852.2206008-1-nipun.gupta@amd.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>