clocksource: timer-riscv: Don't enable/disable timer interrupt

clocksource: timer-riscv: Don't enable/disable timer interrupt

Currently, we enable/disable timer interrupt at runtime to start/stop
timer events. This makes timer interrupt state go out-of-sync with
the Linux interrupt subsystem.

To address the above issue, we can stop a per-HART timer interrupt
by setting U64_MAX in timecmp CSR (or sbi_set_timer()) at the time
of handling timer interrupt.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/r/20230710131902.1459180-2-apatel@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>