[U-Boot] U-boot for 64bit ARMv8

[TigerLiu at viatech.com.cn]

Hi, experts:
I found ARMv8/Exceptions.S only created a 8 items vector table.

But based on ARMv8 Arch Ref Manual, it should create 16 items in a
vector table:
Current Exception level with SP_EL0 : 4 items
Current Exception level with SP_Elx : 4 items
EL immediately lower than target_EL is using AARCH64 : 4 items
EL immediately lower than target_EL is using AARCH32 : 4 items

Are current 8 items enough? Or will patch it in the future?

Best wishes,