riscv: Fix efi header for RV32

RV32 should use PE32 format instead of PE32+ as the efi header format.
This requires following changes
1. A different header magic value
2. An additional parameter known as BaseOfData. Currently, it is set to
   zero in absence of any usage.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Rick Chen <rick@andestech.com>