sparc/vdso: Add helper function for 64-bit right shift on 32-bit target

Add helper function for 64-bit right shift on 32-bit target so that
clang does not emit a runtime library call.

Signed-off-by: Koakuma <koachan@protonmail.com>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/20240808-sparc-shr64-v2-1-fd18f1b2cea9@protonmail.com


Signed-off-by: Andreas Larsson <andreas@gaisler.com>