sparc: move MSI related definitions to where they are used

The definitions in arch/sparc/include/asm/msi.h are only used in
arch/sparc/mm/srmmu.c, so it makes sense to have them in the C file
directly.

In addition, having a custom arch/sparc/include/asm/msi.h prevents
from using the asm-generic version of this header, which is necessary
to be able to include <linux/msi.h> when CONFIG_GENERIC_MSI_IRQ_DOMAIN
is enabled.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>