sim: Fix pseudo instruction parameter loading

sim: Fix pseudo instruction parameter loading

With the new ABI API the position argument of the pseudo inst ABI was
not updated correctly. The position needs to be incremented (at least)
once per argument.

Note: `position++` must be outside of the function call because of a GCC
complaint:
build/X86/sim/pseudo_inst.hh:80:48: error: cannot bind non-const lvalue
reference of type 'int&' to an rvalue of type 'PseudoInstABI::Position
{aka int}'
         return TheISA::getArgument(tc, position++, sizeof(uint64_t),
false);

Issue: https://gem5.atlassian.net/browse/GEM5-351
Change-Id: Idd890a587a565b8ad819f094147a02dc1519e997
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25543
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>