Merge tag 'mips-pull-2020-04-27' of https://gitlab.denx.de/u-boot/custodians/u-boot-mips

- brcmnand: fix missing code path from Linux driver
- bmips: fix build error when disabling USB
- mips: add option to restore original exception vector base
- mips: fix off-by-one error when clearing gd_data
- mips: minor fixes for compatibility with generic SPL framework
- spl: refactor legacy image loading
- spl: add LZMA decompression support for legacy images
- Makefile: add target to build LZMA compressed U-Boot images
- mtmips: refactor and rewrite low-level init code
- mtmips: add and enable SPL support with LZMA
- mtmips: add support for MT7628 reference board
- mtmips: add support for VoCore/VoCore2 board