perf: imx9_perf: make the read-only array mask static const

Don't populate the read-only array mask on the stack at run time,
instead make it static const.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250611133917.170888-1-colin.i.king@gmail.com


Signed-off-by: Will Deacon <will@kernel.org>