arm: axxia: ddr_retention: don't call usleep at atomic context

commit 42aa521f

 from
https://github.com/axxia/linux-yocto.git v5.10/standard/axxia-dev/base.

When running the command:
	#echo 1 > /proc/driver/axxia_ddr_retention_reset
the function usleep_range is called at an atomic context, using udelay
can avoid the calltrace as below:

BUG: scheduling while atomic: sh/519/0x00000002
Modules linked in:
CPU: 12 PID: 519 Comm: sh Not tainted 5.10.75-yocto-standard+ #9
Hardware name: INTEL Axxia
[<c0612444>] (unwind_backtrace) from [<c060c044>] (show_stack+0x18/0x1c)
[<c060c044>] (show_stack) from [<c1034ee4>] (dump_stack+0x98/0xac)
[<c1034ee4>] (dump_stack) from [<c0657900>] (__schedule_bug+0x78/0x8c)
[<c0657900>] (__schedule_bug) from [<c103cc04>] (__schedule+0x454/0x648)
[<c103cc04>] (__schedule) from [<c103ce90>] (schedule+0x98/0x120)
[<c103ce90>] (schedule) from [<c1041384>] (schedule_hrtimeout_range_clock+0xcc/0x15c)
[<c1041384>] (schedule_hrtimeout_range_clock) from [<c1041434>] (schedule_hrtimeout_range+0x20/0x28)
[<c1041434>] (schedule_hrtimeout_range) from [<c1040c64>] (usleep_range+0x74/0xa4)
[<c1040c64>] (usleep_range) from [<c0623290>] (axxia_ddr_retention_trigger+0x10/0x1c)
[<c0623290>] (axxia_ddr_retention_trigger) from [<c08a4c0c>] (proc_reg_write+0xb0/0xd4)
[<c08a4c0c>] (proc_reg_write) from [<c081260c>] (vfs_write+0xd4/0x464)
[<c081260c>] (vfs_write) from [<c0813ed4>] (ksys_write+0x6c/0xf8)
[<c0813ed4>] (ksys_write) from [<c0600060>] (ret_fast_syscall+0x0/0x4c)
Exception stack(0xc566dfa8 to 0xc566dff0)
dfa0:                   00000002 0058c048 00000001 0058c048 00000002 00000000
dfc0: 00000002 0058c048 b6fcd480 00000004 b6f59c60 00000000 0056ac00 00000000
dfe0: 00000004 beb03918 b6eef459 b6e70386

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Liwei Song <liwei.song@windriver.com>