Revert "ARM: 6943/1: mm: use TTBR1 instead of reserved context ID"

Revert "ARM: 6943/1: mm: use TTBR1 instead of reserved context ID"

This reverts commit 52af9c6cd863fe37d1103035ec7ee22ac1296458.

Will Deacon reports that:

 In 52af9c6c ("ARM: 6943/1: mm: use TTBR1 instead of reserved context ID")
 I updated the ASID rollover code to use only the kernel page tables
 whilst updating the ASID.

 Unfortunately, the code to restore the user page tables was part of a
 later patch which isn't yet in mainline, so this leaves the code
 quite broken.

We're also in the process of eliminating __ARCH_WANT_INTERRUPTS_ON_CTXSW
from ARM, so lets revert these until we can properly sort out what we're
doing with the ARM context switching.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>