x86/mm: Avoid redundant interrupt disable in load_mm_cr4()

load_mm_cr4() is always called with interrupts disabled from:

 - switch_mm_irqs_off()
 - refresh_pce(), which is a on_each_cpu() callback

Thus, disabling interrupts in cr4_set/clear_bits() is redundant.

Implement cr4_set/clear_bits_irqsoff() helpers, rename load_mm_cr4() to
load_mm_cr4_irqsoff() and use the new helpers. The new helpers do not need
a lockdep assert as __cr4_set() has one already.

The renaming in combination with the checks in __cr4_set() ensure that any
changes in the boundary conditions at the call sites will be detected.

[ tglx: Massaged change log ]

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/0fbbcb64-5f26-4ffb-1bb9-4f5f48426893@siemens.com