powerpc/mpc85xx: call k(un)map_atomic rather than k(un)map

powerpc/mpc85xx: call k(un)map_atomic rather than k(un)map

The k(un)map function may be called in atomic context in the
function map_and_flush(), so use k(un)map_atomic to replace it,
else we would get the below warning during kdump:

BUG: sleeping function called from invalid context at include/linux/highmem.h:58
in_atomic(): 1, irqs_disabled(): 1, pid: 736, name: sh
INFO: lockdep is turned off.
irq event stamp: 0
hardirqs last  enabled at (0): [<          (null)>]           (null)
hardirqs last disabled at (0): [<c000000000066d1c>] .copy_process.part.44+0x50c/0x1360
softirqs last  enabled at (0): [<c000000000066d1c>] .copy_process.part.44+0x50c/0x1360
softirqs last disabled at (0): [<          (null)>]           (null)
CPU: 1 PID: 736 Comm: sh Tainted: G      D W    3.10.62-ltsi-WR6.0.0.0_standard #2
Call Trace:
[c0000000f47cf120] [c00000000000b150] .show_stack+0x170/0x290 (unreliable)
[c0000000f47cf210] [c000000000b71334] .dump_stack+0x28/0x3c
[c0000000f47cf280] [c0000000000bb5d8] .__might_sleep+0x1a8/0x270
[c0000000f47cf310] [c0000000000440cc] .map_and_flush+0x4c/0xc0
[c0000000f47cf390] [c0000000000441cc] .mpc85xx_smp_machine_kexec+0x8c/0xec0
[c0000000f47cf420] [c00000000002ae00] .machine_kexec+0x60/0x90
[c0000000f47cf4b0] [c00000000010957c] .crash_kexec+0x8c/0x100
[c0000000f47cf6a0] [c000000000015df8] .die+0x348/0x450
[c0000000f47cf740] [c00000000002f3a0] .bad_page_fault+0xe0/0x130
[c0000000f47cf7c0] [c00000000001f3e4] storage_fault_common+0x40/0x44

Signed-off-by: Yanjiang Jin <yanjiang.jin@windriver.com>
[scottwood@freescale.com: fix subject line]
Signed-off-by: Scott Wood <scottwood@freescale.com>