*/fsp/exit_car: Push stack address into %esp

*/fsp/exit_car: Push stack address into %esp

Fixes: 5315e96abf ("arch/x86/postcar: Use a separate stack for C execution")
Resolves:
https://mail.coreboot.org/hyperkitty/list/coreboot@coreboot.org/
thread/TGIWAKZKELJRAEMKJNYRJ55MX2CXYNCV/
Link: https://mail.coreboot.org/hyperkitty/list/coreboot@coreboot.org/
thread/2JC3GNJSGXUD6DRVUY7O2O3W6OM3E2MY/

5315e96abf broke platforms using FSP-M to tear down CAR. It was pushing
the value at '_estack' into %esp rather than the address '_estack'.

Change-Id: Ie1fc70bd60fe3a2519ffb71625a35630fa732ff6
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65716
Reviewed-by: Patrick Georgi <patrick@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Raul Rangel <rrangel@chromium.org>