riscv: vdso: Drop CONFIG_GENERIC_TIME_VSYSCALL guard around syscall fallbacks

riscv: vdso: Drop CONFIG_GENERIC_TIME_VSYSCALL guard around syscall fallbacks

The syscall definitions can be built just fine for 32-bit systems.
Also the guard does not cover __arch_get_hw_counter() which is always
used together with those system call fallbacks. Also this header is
unused when no vDSO is built anyways.

Drop the ifdeffery. The logic will be simpler to understand. Furthermore
this prepares the complete removal of CONFIG_GENERIC_TIME_VSYSCALL.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260519-vdso-generic_time_vsyscal-v1-1-5c2a5905d5f5@linutronix.de