Update CHANGELOG.md for 3.4.0
Update CHANGELOG.md for 3.4.0

Signed-off-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org>
Tested-by: Akshay Bhat <124e9ed437bdfdc15bb6080f285761d3d4b394cb@timesys.com> (Atmel SAM)
Tested-by: Bryan O'Donoghue <165dc05575478af93ac2f97f67be6e1756010094@linaro.org> (i.MX7Solo WaRP7)
Tested-by: Etienne Carriere <f21bc5b8f3ea1962eb45af359f1abea6578cab94@linaro.org> (b2260, GP)
Tested-by: Etienne Carriere <f21bc5b8f3ea1962eb45af359f1abea6578cab94@linaro.org> (stm32mp1, GP)
Tested-by: Igor Opaniuk <ca782e5848fbe7ab0a250faa8ae33b643dd89a09@linaro.org> (Poplar)
Tested-by: Igor Opaniuk <ca782e5848fbe7ab0a250faa8ae33b643dd89a09@linaro.org> (RPi3)
Tested-by: Jens Wiklander <7706914404370d7502c27a0eff493dcf491feb51@linaro.org> (FVP)
Tested-by: Jens Wiklander <7706914404370d7502c27a0eff493dcf491feb51@linaro.org> (Hikey)
Tested-by: Jens Wiklander <7706914404370d7502c27a0eff493dcf491feb51@linaro.org> (Juno)
Tested-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org> (HiKey960, GP)
Tested-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org> (QEMU)
Tested-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org> (QEMUv8)
Tested-by: Rouven Czerwinski <76cf81876f6bd9c36f3e19bf926d3e7bc1d0dc80@pengutronix.de> (mx6qsabresd)
Tested-by: Sumit Garg <0904b466d9452daa97eb086f40b9aaa7e498e972@linaro.org> (Developerbox)
Tested-by: Victor Chong <4aabb03bd6dd29c44a49684d87b08ac07e10b492@linaro.org> (HiKey960 AOSP P, HiKey620 AOSP P)
Tested-by: Volodymyr Babchuk <07adff7e050dc3230ac0b7d9c296bbb62f4ecc95@gmail.com> (RCAR H3)
Tested-by: Ying-Chun Liu (PaulLiu) <b2208d5e3abe8ebd68b9a2a6b6e7f25949a99af3@linaro.org> (sunxi-bpi_zero)

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os