meta-ampere: mtjade: switch to use u-boot 2019.04

u-boot 2016.07 does not work well with 64MB SPI-NOR layout, which has
the following issues:
- Incorrect environment variable configuration which makes fail to boot
to kernel and has fw_setenv/fw_getenv commands not work.
- Even update the patch in meta-phosphor to fix above issue, still has
issue with setting environment variable in Linux which makes factory
reset failure each 2 times.
This commit changes to use u-boot 2019.04 to fix above issue.

Tested:
1. Do factory reset and check if the BMC can boot to kernel.
2. Trigger factory reset via Redfish multiple times (6 times) and verify
if the factory reset action can be executed at all times.

Signed-off-by: Thang Q. Nguyen <thang@os.amperecomputing.com>
Change-Id: Ibb269d96a2e2b509aeccbeeaa130aad57093d139