tests: Move ISA-independent tests to the NULL ISA

tests: Move ISA-independent tests to the NULL ISA

This patch simply takes a first step to use the NULL ISA build for
tests that do not make use of a CPU. Most of the Ruby tests could go
the same way, but to avoid duplicating a lot of compilation targets
that will have to wait until Ruby is built as a library and linked in
independently.

--HG--
rename : tests/quick/se/50.memtest/ref/alpha/linux/memtest/config.ini => tests/quick/se/50.memtest/ref/null/none/memtest/config.ini
rename : tests/quick/se/50.memtest/ref/alpha/linux/memtest/simerr => tests/quick/se/50.memtest/ref/null/none/memtest/simerr
rename : tests/quick/se/50.memtest/ref/alpha/linux/memtest/simout => tests/quick/se/50.memtest/ref/null/none/memtest/simout
rename : tests/quick/se/50.memtest/ref/alpha/linux/memtest/stats.txt => tests/quick/se/50.memtest/ref/null/none/memtest/stats.txt
rename : tests/quick/se/70.tgen/ref/arm/linux/tgen-simple-dram/simerr => tests/quick/se/70.tgen/ref/null/none/tgen-simple-dram/simerr
rename : tests/quick/se/70.tgen/ref/arm/linux/tgen-simple-dram/simout => tests/quick/se/70.tgen/ref/null/none/tgen-simple-dram/simout
rename : tests/quick/se/70.tgen/ref/arm/linux/tgen-simple-dram/stats.txt => tests/quick/se/70.tgen/ref/null/none/tgen-simple-dram/stats.txt
rename : tests/quick/se/70.tgen/ref/arm/linux/tgen-simple-mem/simerr => tests/quick/se/70.tgen/ref/null/none/tgen-simple-mem/simerr
rename : tests/quick/se/70.tgen/ref/arm/linux/tgen-simple-mem/simout => tests/quick/se/70.tgen/ref/null/none/tgen-simple-mem/simout
rename : tests/quick/se/70.tgen/ref/arm/linux/tgen-simple-mem/stats.txt => tests/quick/se/70.tgen/ref/null/none/tgen-simple-mem/stats.txt