x86/ibrs: Remove 'ibrs_dump' and remove the pr_debug

x86/ibrs: Remove 'ibrs_dump' and remove the pr_debug

Orabug: 27351274

There is no business in having ibrs_dump exposed to user-space
and it allowing to write to it. Reading that entry ends up
doing an IPI across all CPUs reading an MSR and that (on large
machines) is not something user-space should be able to do.

And also remove the pr_debug statements.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>