riscv: Support standalone

riscv: Support standalone

Run hello_world successfully.

U-Boot 2018.01-rc2-00033-gb265b91-dirty (Dec 22 2017 - 13:54:21 +0800)

DRAM:  1 GiB
MMC:   mmc@f0e00000: 0
SF: Detected mx25u1635e with page size 256 Bytes, erase size 4 KiB, total 2 MiB
In:    serial@f0300000
Out:   serial@f0300000
Err:   serial@f0300000
Net:
Warning: mac@e0100000 (eth0) using random MAC address - 0a:47:9b:f8:b4:f2
eth0: mac@e0100000
RISC-V # mmc rescan
RISC-V # fatls mmc 0:1
318907   u-boot-ae250-64.bin
1252   hello_world_ae250_32.bin
328787   u-boot-ae250-32.bin

3 file(s), 0 dir(s)

RISC-V # fatload mmc 0:1 0x600000 hello_world_ae250_32.bin
reading hello_world_ae250_32.bin
1252 bytes read in 23 ms (52.7 KiB/s)
RISC-V # go 0x600000
Example expects ABI version 9
Actual U-Boot ABI version 9
Hello World
argc = 1
argv[0] = "0x600000"
argv[1] = "$B@"
Hit any key to exit ...

RISC-V #

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Signed-off-by: Greentime Hu <green.hu@gmail.com>