lib: sbi: Disable interrupt during config matching

PMU overflow interrupt should be disabled durinig initial configuration of
counters. They should be enabled while starting counters.

Fixes: 730f01bb

 ("lib: sbi: Support sscofpmf extension in OpenSBI")
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>