[SPI-2020] deffinition of 101_ATLAS_4

There is a new request for new layer LCG_101_ATLAS_4 from ATLAS.

it should include/have:

• EvtGen 2.1.1 (SPI-2014)

• the latest version of valgrind 3.18.1

• the latest version of TheP8I (SPI-2005)

• based on LCG_101_ATLAS_2, i.e. built against HepMC2

• cuda and cudnn from LCG_101_ATLAS_3