perf kbuild: fix a typo bug

Bad option passed to linux/scripts/config so as to enable
CONFIG_LIBELF_MINIMAL (-E instead of -e)
perf kbuild: fix missing cleanings of feature-check binaries
perf kbuild: compile x86 dwarf code only if libdwarf is detected
perf kbuild: add missing uses of CROSS_COMPILE variables

The variable CROSS_COMPILE was not used to define AS, CC, ...
The variable CROSS_COMPILE was not stored in .config-detected
perf kbuild: add missing Kbuild files for powerpc architecture