Update CHANGELOG for 3.12.0 and collect Tested-by tags.

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Tested-by: Clement Faure <clement.faure@nxp.com> (mx6dlsabreauto)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx6dlsabresd)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx6qpsabreauto)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx6sllevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx6ulevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx6ullevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx6ulzevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx7dsabresd)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx7ulpevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx8mmevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx8mnevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx8mqevk)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx8qmmek)
Tested-by: Clement Faure <clement.faure@nxp.com> (mx8qxpmek)
Tested-by: Etienne Carriere <etienne.carriere@linaro.org> (stm32mp1)
Tested-by: Igor Opaniuk <igor.opaniuk@gmail.com> (Poplar)
Tested-by: Jens Wiklander <jens.wiklander@linaro.org> (FVP)
Tested-by: Jens Wiklander <jens.wiklander@linaro.org> (Juno)
Tested-by: Jerome Forissier <jerome@forissier.org> ((HiKey GP) # issue 4324)
Tested-by: Jerome Forissier <jerome@forissier.org> ((HiKey960 GP) # issue 4324)
Tested-by: Jerome Forissier <jerome@forissier.org> (QEMU)
Tested-by: Jerome Forissier <jerome@forissier.org> (QEMUv8)
Tested-by: Joakim Bech <joakim.bech@linaro.org> (RPi3B)
Tested-by: Joakim Bech <joakim.bech@linaro.org> (RPi3B-NFS)
Tested-by: Ricardo Salveti <ricardo@foundries.io> (ZynqMP)
Tested-by: Rouven Czerwinski <r.czerwinski@pengutronix.de> (imx-ccimx6ulsbcpro)
Tested-by: Rouven Czerwinski <r.czerwinski@pengutronix.de> (imx-mx6qsabrelite)
Tested-by: Sumit Garg <sumit.garg@linaro.org> (Developerbox)
Tested-by: Victor Chong <victor.chong@linaro.org> (HiKey960 AOSP P)
Tested-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com> (Rcar H3)
Tested-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com> (Rcar H3/virtualization)