arch: mips: Update initrd_start and initrd_end

arch: mips: Update initrd_start and initrd_end

Microsemi SoC defines CONFIG_SYS_SDRAM_BASE to be 0x80000000, which
represents the start of kseg0 and represents a virtual address. Meaning
that the initrd_start and initrd_end point somewhere kseg0.
When these parameters are passed to linux kernel through DT
they are pointing somewhere in kseg0 which is a virtual address but linux
kernel expects the addresses to be physical addresses(in kuseg) because
it is converting the physical address to a virtual one.

Therefore update the uboot to pass the physical address of initrd_start
and initrd_end by converting them using the function virt_to_phys before
setting up the DT.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>