ChromeOS: Refactor SMBIOS type0 bios_version()

Pointer to an empty string (filled with spaces) is
stored inside GNVS. Rearrange things to avoid having
<chromeos/gnvs.h> in SMBIOS code.

Change-Id: I9405afbea29b896488b4cdd6dd32c4db686fe48c
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49281
Reviewed-by: Lance Zhao
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/smbios.h

@@ -55,6 +55,9 @@ const char *smbios_chassis_version(void);
 const char *smbios_chassis_serial_number(void);
 const char *smbios_processor_serial_number(void);
 
+/* This string could be filled late in payload. */
+void smbios_type0_bios_version(uintptr_t address);
+
 void smbios_ec_revision(uint8_t *ec_major_revision, uint8_t *ec_minor_revision);
 
 unsigned int smbios_memory_error_correction_type(struct memory_info *meminfo);