MIPS: Allows relocation exception vectors everywhere

Now the exception vector for CPS systems are allocated on-fly
with memblock as well.

It will try to allocate from KSEG1 first, and then try to allocate
in low 4G if possible.

The main reset vector is now generated by uasm, to avoid tons
of patches to the code. Other vectors are copied to the location
later.

    move 64bits fix in an other patch
    fix cache issue with mips_cps_core_entry
    rewrite the patch to reduce the diff stat
    move extern in header
    use cache address for copying vector

gc: use the new macro CKSEG[0A1]DDR_OR_64BIT()
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>