riscv: Explicitly pass -march and -mabi to the compiler

riscv: Explicitly pass -march and -mabi to the compiler

At present the compiler flag against which architecture and abi
variant the riscv image is built for is not explicitly indicated
which means the default compiler configuration is used. But this
does not work if we want to build a different target (eg: 32-bit
riscv images using a toolchain configured for 64-bit riscv).

Fix this by explicitly passing -march and -mabi to the compiler.
Since generically we don't use floating point in U-Boot, specify
the RV[32|64]IMA ISA and software floating ABI.

This also fix some alignment coding style issues.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>