MIPS: spaces: Define a couple of handy macros

Define CKSEGX_SIZE to represent the size of each KSEG segment.

Introduce CKSEG0ADDR_OR_64BIT and CKSEG1ADDR_OR_64BIT to get an XPHYS
address in 64bits and CKSEG[01]ADDR() in 32 bits mode.

Co-developed-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>