LiveOPP: add PLLDDR boost interface

Thanks @cocafe for idea and original patch.
I found way to overclock PLLDDR stably upto 975 MHz (on my codina).
To use this interface type command like that:
`echo 0x0005017f > /sys/kernel/liveopp/pllddr # 975 MHz`
Please note only values that starts with 0x0005.... are allowed.

I did some tests that confirmed better RAM performance:
Governor - performance, CPU 1200 MHz.

1) Memory speed benchmark:
  a) 798 MHz

Reading speed in MBytes/second
Memory    x[m]=x[m]+s*y[m]            x[m]=x[m]+y[m]
Kbytes      Dble    Sngl     Int           Dble    Sngl     Int
   16       1735     886    2381           2719    1360    2808
   32       1586     819    1760           1991    1145    1953
   64       1459     755    1279           1580     978    1410
  128       1454     763    1223           1589     978    1345
  256       1449     760    1183           1579     975    1298
  512        940     697     934           1161     867     979
 1024        480     443     463            489     457     490
 4096        378     350     351            395     364     380
16384        402     353     397            389     382     391
65536        388     364     399            400     392     408

Total elapsed time: 12.9 seconds

  b) 975 MHz

Reading speed in MBytes/second
Memory    x[m]=x[m]+s*y[m]            x[m]=x[m]+y[m]
Kbytes      Dble    Sngl     Int           Dble    Sngl     Int
   16       1737     889    2449           2720    1365    2804
   32       1600     824    1762           2006    1146    1958
   64       1457     756    1286           1576     979    1404
  128       1456     762    1224           1591     979    1347
  256       1449     762    1193           1584     977    1292
  512       1204     712     997           1274     901    1010
 1024        573     524     575            538     540     582
 4096        459     411     335            410     423     452
16384        455     434     458            482     435     471
65536        454     437     456            487     454     461

Total elapsed time: 12.0 seconds

2) random access benchmark:
 a) 798 MHz

Mbytes/Second transferring  4 byte words:

Memory           Serial.........    Random.........
Kbytes           Read     Rd/Wrt    Read     Rd/Wrt
   16            2788       3013    2787     3033
   32            1879       1963    1745     2130
   64            1103       1110    1029     1166
  128             988        972     787      844
  256             938        970     641      671
  512             855        738     236      275
 1024             627        415     110       89
 4096             570        376      69       68
16384             573        367      59       58
65536             508        395      51       49

Total elapsed time: 12.2 seconds

b) 975 MHz

Mbytes/Second transferring  4 byte words:

Memory           Serial.........    Random.........
Kbytes           Read     Rd/Wrt    Read     Rd/Wrt
   16            2779       3031    2785     3030
   32            1878       1959    1734     2150
   64            1101       1099    1034     1165
  128             986        993     812      853
  256             976        981     582      713
  512             886        771     289      311
 1024             657        541     129      125
 4096             643        429      89       79
16384             643        467      72       69
65536             597        475      59       59

Total elapsed time: 11.5 seconds

mentioned benchmarks were found on
http://www.roylongbottom.org.uk/android%20benchmarks.htm

Signed-off-by: Shilin Victor <chrono.monochrome@gmail.com>

https://github.com/cocafe/i9070_kernel_CoCore-E/commit/f3dc15cb92b355736e47e0d0405cc9f1217d79d8