I skipped the following files because they were not simple.
I'll create separate PRs.
arch/xtensa/src/esp32/esp32_cpustart.c
arch/xtensa/src/common/xtensa_abi.h
boards/xtensa/esp32/esp32-core/include/board.h
Also, I skipped the following files and directories because
they looked too huge and/or foreign.
arch/xtensa/include/esp32/tie.h
arch/xtensa/include/xtensa/xtensa_corebits.h
arch/xtensa/src/esp32/hardware/
arch/xtensa/include/esp32/tie-asm.h
arch/xtensa/include/esp32/core-isa.h
arch/xtensa/include/xtensa/core.h
I also fixed a few "is is" style typos when unwrapping long lines.
