arch/x86/boot: Jump to payload in protected mode

*   On ARCH_RAMSTAGE_X86_64 jump to the payload in protected mode.
*   Add a helper function to jump to arbitrary code in protected mode,
    similar to the real mode call handler.
*   Doesn't affect existing x86_32 code.
*   Add a macro to cast pointer to uint32_t that dies if it would overflow
    on conversion

Tested on QEMU Q35 using SeaBIOS as payload.
Tested on Lenovo T410 with additional x86_64 patches.

Change-Id: I6552ac30f1b6205e08e16d251328e01ce3fbfd14
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/30118
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/include/assert.h

@@ -80,4 +80,15 @@ extern void _dead_code_assertion_failed(void) __attribute__((noreturn));
 	*(type *)(uintptr_t)0; \
 })
 
+#ifdef __x86_64__
+#define pointer_to_uint32_safe(x) ({ \
+	if ((uintptr_t)(x) > 0xffffffffUL) \
+		die("Cast from pointer to uint32_t overflows"); \
+	(uint32_t)(uintptr_t)(x); \
+})
+#else
+#define pointer_to_uint32_safe(x) ({ \
+	(uint32_t)(uintptr_t)(x); \
+})
+#endif
 #endif // __ASSERT_H__