[CodeGen] Change 'Scalar' to 'Array' in method names. NFC.

generateScalarLoad() and generateScalarStore() are used for explicit (MK_Array)
memory accesses, therefore the method names were misleading. The names also
were similar to generateScalarLoads() and generateScalarStores() (plural forms)
which indeed handle scalar accesses. Presumbly, they were originally named to
contrast VectorBlockGenerator::generateLoad().

Rename the two methods to generateArrayLoad(),
respectively generateArrayStore().

llvm-svn: 282861