rk: ddr_freq: version 2.1

rk: ddr_freq: version 2.1

fix this bug:
BUG: scheduling while atomic: ddrfreqd/65/0x00000002
[<c043e504>] (unwind_backtrace+0x0/0xf8) from [<c08fe368>] (__schedule+0x7ec/0x8a8)
[<c08fe368>] (__schedule+0x7ec/0x8a8) from [<c08ff620>] (__mutex_lock_slowpath+0x128/0x1bc)
[<c08ff620>] (__mutex_lock_slowpath+0x128/0x1bc) from [<c08ff720>] (mutex_lock+0x6c/0x70)
[<c08ff720>] (mutex_lock+0x6c/0x70) from [<c045328c>] (ddr_scale_rate_for_dvfs+0x30/0x16c)
[<c045328c>] (ddr_scale_rate_for_dvfs+0x30/0x16c) from [<c044da6c>] (dvfs_target+0x12c/0x1a0)
[<c044da6c>] (dvfs_target+0x12c/0x1a0) from [<c0453b10>] (dvfs_set_rate+0x48/0x68)
[<c0453b10>] (dvfs_set_rate+0x48/0x68) from [<c0453504>] (ddrfreq_mode+0x70/0xc4)
[<c0453504>] (ddrfreq_mode+0x70/0xc4) from [<c04536c8>] (ddrfreq_task+0x38/0x160)
[<c04536c8>] (ddrfreq_task+0x38/0x160) from [<c048a704>] (kthread+0x80/0x88)
[<c048a704>] (kthread+0x80/0x88) from [<c04399c8>] (kernel_thread_exit+0x0/0x8)