nvme: extend help message when mmap regs fails

nvme: extend help message when mmap regs fails

Newer kernels enable the lockdown feature when secure boot is enabled.
This feature also prevents the register mapping into userspace. Thus it
is not enough to have CONFIG_IO_STRICT_DEVMEM disabled. Extend the
message with the hint also to disable secure boot.

While at it, also lower the reporting level to INFO, so that one single
'-v' is enough to get this information.

Signed-off-by: Daniel Wagner <dwagner@suse.de>