drm/nouveau/kms/gv100: use static for gv100_disp_core_mthd_[base|sor]

Sparse reports these issues
coregv100.c:27:1: warning: symbol 'gv100_disp_core_mthd_base' was not declared. Should it be static?
coregv100.c:43:1: warning: symbol 'gv100_disp_core_mthd_sor' was not declared. Should it be static?

These variables are only used in coregv100.c.  Single file use
variables should be static, so add static to their storage-class specifier.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220422185132.3163248-1-trix@redhat.com