ARM: 6066/1: Fix "BUG: scheduling while atomic: swapper/0/0x00000002

This patch fixes the preempt leak in the cpuidle path invoked from
cpu-hotplug. The fix is suggested by Russell King and is based
on x86 idea of calling init_idle() on the idle task when it's
re-used which also resets the preempt count amongst other things

dump:
BUG: scheduling while atomic: swapper/0/0x00000002
Modules linked in:
Backtrace:
[<c0024f90>] (dump_backtrace+0x0/0x110) from [<c0173bc4>] (dump_stack+0x18/0x1c)
 r7:c02149e4 r6:c033df00 r5:c7836000 r4:00000000
[<c0173bac>] (dump_stack+0x0/0x1c) from [<c003b4f0>] (__schedule_bug+0x60/0x70)
[<c003b490>] (__schedule_bug+0x0/0x70) from [<c0174214>] (schedule+0x98/0x7b8)
 r5:c7836000 r4:c7836000
[<c017417c>] (schedule+0x0/0x7b8) from [<c00228c4>] (cpu_idle+0xb4/0xd4)
# [<c0022810>] (cpu_idle+0x0/0xd4) from [<c0171dd8>] (secondary_start_kernel+0xe0/0xf0)
 r5:c7836000 r4:c0205f40
[<c0171cf8>] (secondary_start_kernel+0x0/0xf0) from [<c002d57c>] (prm_rmw_mod_reg_bits+0x88/0xa4)
 r7:c02149e4 r6:00000001 r5:00000001 r4:c7836000
Backtrace aborted due to bad frame pointer <c7837fbc>

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>