riscv: use log functions in fdt_fixup

Replace printf() and debug() by log_err() and log_debug().

"No reserved memory region found in source FDT\n" is not an error but a
debug information.

%s/can not/cannot/ - use the more common spelling.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>