x86: bios_uv.c: uv_systab should be static

Impact: cleanup, reduce kernel size a bit, avoid sparse warning

Fixes sparse warning:
arch/x86/kernel/bios_uv.c:28:18: warning: symbol 'uv_systab' was not declared. Should it be static?

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>