vfio: platform: mark symbols static where possible

vfio: platform: mark symbols static where possible

We get a few warnings when building kernel with W=1:
drivers/vfio/platform/vfio_platform_common.c:76:5: warning: no previous prototype for 'vfio_platform_acpi_call_reset' [-Wmissing-prototypes]
drivers/vfio/platform/vfio_platform_common.c:98:6: warning: no previous prototype for 'vfio_platform_acpi_has_reset' [-Wmissing-prototypes]
drivers/vfio/platform/vfio_platform_common.c:640:5: warning: no previous prototype for 'vfio_platform_of_probe' [-Wmissing-prototypes]
drivers/vfio/platform/reset/vfio_platform_amdxgbe.c:59:5: warning: no previous prototype for 'vfio_platform_amdxgbe_reset' [-Wmissing-prototypes]
drivers/vfio/platform/reset/vfio_platform_calxedaxgmac.c:60:5: warning: no previous prototype for 'vfio_platform_calxedaxgmac_reset' [-Wmissing-prototypes]
....

In fact, these functions are only used in the file in which they are
declared and don't need a declaration, but can be made static.
so this patch marks these functions with 'static'.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Baptiste Reynal <b.reynal@virtualopensystems.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>