sparc64: vdso: Move syscall fallbacks into header

sparc64: vdso: Move syscall fallbacks into header

The generic vDSO libraries expected the syscall fallbacks in
asm/vdso/gettimeofday.h. To prepare the adoption of the generic library,
move the existing functions there.

While at it, rename them so they match what the generic library expects.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Andreas Larsson <andreas@gaisler.com>
Link: https://patch.msgid.link/20260304-vdso-sparc64-generic-2-v6-8-d8eb3b0e1410@linutronix.de