drm/xe: Move vm bind bo validation to a helper function

Move vm bind bo validation to a helper function to make the
xe_vm_bind_ioctl() more readable.

v2: Capture ret value of xe_vm_bind_ioctl_validate_bo(Matt B).
    Remove redundant coh_mode param.

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Oak Zeng <oak.zeng@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240430162529.21588-3-nirmoy.das@intel.com
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>