libpayload: Save EAX and EBX only for multiboot payloads

When CONFIG_LP_MULTIBOOT is enabled, save the values of EAX and EBX
passed from the bootloader. This information can be useful for
multiboot payloads feature alone.

Change-Id: I98c2cd00206ee48eb0fc67edd9533032bcf3e5eb
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82040
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
Reviewed-by: Dinesh Gehlot <digehlot@google.com>

payloads/libpayload/arch/x86/main.c

@@ -30,9 +30,6 @@
 #include <libpayload.h>
 #include <arch/apic.h>
 
-unsigned long loader_eax;  /**< The value of EAX passed from the loader */
-unsigned long loader_ebx;  /**< The value of EBX passed from the loader */
-
 int main_argc;    /**< The argc value to pass to main() */
 
 /** The argv value to pass to main() */