Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream-kconfig' into staging

Initial Kconfig work, excluding ARM and MIPS

# gpg: Signature made Thu 07 Mar 2019 20:54:27 GMT
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "[email protected]"
# gpg: Good signature from "Paolo Bonzini <[email protected]>" [full]
# gpg:                 aka "Paolo Bonzini <[email protected]>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream-kconfig: (54 commits)
  kconfig: add documentation
  .travis.yml: test that no-default-device builds do not regress
  xtensa-softmmu.mak: express dependencies with Kconfig
  unicore32-softmmu.mak: express dependencies with Kconfig
  sparc64-softmmu.mak: express dependencies with Kconfig
  sparc-softmmu.mak: express dependencies with Kconfig
  sh4-softmmu.mak: express dependencies with Kconfig
  s390x: express dependencies with Kconfig
  riscv-softmmu.mak: replace CONFIG_* with Kconfig "select" directives
  or1k-softmmu.mak: express dependencies with Kconfig
  nios2-softmmu.mak: express dependencies with Kconfig
  moxie-softmmu.mak: express dependencies with Kconfig
  microblaze-softmmu.mak: express dependencies with Kconfig
  m68k-softmmu.mak: express dependencies with Kconfig
  lm32-softmmu.mak: express dependencies with Kconfig
  hppa-softmmu.mak: express dependencies with Kconfig
  cris-softmmu.mak: express dependencies with Kconfig
  alpha-softmmu.mak: express dependencies with Kconfig
  ppc: Express dependencies of the embedded machines with kconfig
  ppc: Express dependencies of the Sam460EX machines with kconfig
  ...

Signed-off-by: Peter Maydell <[email protected]>