ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on pre-ARMv6 CPUs

ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on pre-ARMv6 CPUs

This patch removes the __ARCH_WANT_INTERRUPTS_ON_CTXSW definition for
ARMv5 and earlier processors. On such processors, the context switch
requires a full cache flush. To avoid high interrupt latencies, this
patch defers the mm switching to the post-lock switch hook if the
interrupts are disabled.

Reviewed-by: Will Deacon <[email protected]>
Tested-by: Will Deacon <[email protected]>
Reviewed-by: Frank Rowand <[email protected]>
Tested-by: Marc Zyngier <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>