KVM: Mark halt poll and other module parameters with appropriate memory attributes

KVM: Mark halt poll and other module parameters with appropriate memory attributes

Add '__read_mostly' to the halt polling parameters (halt_poll_ns,
halt_poll_ns_grow, halt_poll_ns_grow_start, halt_poll_ns_shrink) since
they are frequently read in hot paths (e.g., vCPU halt handling) but only
occasionally updated via sysfs. This improves cache locality on SMP
systems.

Conversely, mark 'allow_unsafe_mappings' and 'enable_virt_at_load' with
'__ro_after_init', as they are set only during module initialization via
kernel command line or early sysfs writes and remain constant thereafter.
This enhances security by preventing runtime modification and enables
compiler optimizations.

Signed-off-by: Li RongQing <lirongqing@baidu.com>
Link: https://patch.msgid.link/20260210062143.1739-1-lirongqing@baidu.com
Signed-off-by: Sean Christopherson <seanjc@google.com>