[coreboot] [v3][patch] Fix stdcall for asm to C call.

[Marc Jones]

Coreboot uses the compiler option -mregparm=3 which causes variables to be
passed in registers. This is good for size and speed but not good when we
call a C function from asm. Force stage1_phase1 to use stdcall and get
variables off the stack.

Note that I didn't change stage1_phase3 because it doesn't use any variables.

Signed-off-by: Marc Jones