Test: Move test payload related code out of interface header

Test payload uses an SBI call and uses the macros defined in interface
header which is not the correct place to have these definitions.
The interface header file should be used to keep SBI specification
related macros.

Keep all the test payload related code in test itself.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>