TESTING: PM: EM: Add example EM runtime modification module

Add kernel module which allows to modify EM from the user-space.

Example usage:
1. Read
dev:/ # cat /sys/kernel/energy_model_mod/cpu7/em_mod
p=83211 f=500000 pf=182 c=4572
p=182885 f=851000 pf=311 c=5880
p=224914 f=984000 pf=359 c=6265
p=280820 f=1106000 pf=404 c=6950
p=357200 f=1277000 pf=466 c=7665
p=429860 f=1426000 pf=521 c=8250
p=521290 f=1582000 pf=578 c=9018
p=638015 f=1745000 pf=637 c=10015
p=712881 f=1826000 pf=667 c=10687
p=890737 f=2048000 pf=748 c=11908
p=1042097 f=2188000 pf=799 c=13042
p=1120721 f=2252000 pf=823 c=13617
p=1281037 f=2401000 pf=877 c=14607
p=1449075 f=2507000 pf=916 c=15819
p=1685650 f=2630000 pf=961 c=17540
p=1846578 f=2704000 pf=988 c=18690
p=2104739 f=2802000 pf=1024 c=20554

2. Write
echo "p=83211 f=500000 pf=182,p=182885 f=851000 pf=311,p=224914 f=984000 pf=359,p=280820 f=1106000 pf=404,p=357200 f=1277000 pf=466,p=429860 f=1426000 pf=521,p=521290 f=1582000 pf=578,p=638015 f=1745000 pf=637,p=712881 f=1826000 pf=667,p=890737 f=2048000 pf=748,p=1042097 f=2188000 pf=799,p=1120721 f=2252000 pf=823,p=1281037 f=2401000 pf=877,p=1449075 f=2507000 pf=916,p=1685650 f=2630000 pf=961,p=1846578 f=2704000 pf=998,p=2504739 f=2802000 pf=1024" >  /sys/kernel/energy_model_mod/cpu7/em_mod

Change-Id: Ic450ad0435f68d898a4335b4e478134e64c379b5
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>