autoboot.c: Fill env vars in process_fdt_options() only if TEXT_BASE is set

autoboot.c: Fill env vars in process_fdt_options() only if TEXT_BASE is set

The x86 build target "efi-x86" has no TEXT_BASE configured. And with the
introduction of CONFIG_BOOTDELAY for x86, this function is now called
for this board as well. Resulting in compile errors for this target.

Without TEXT_BASE it makes no sense to fill these values. So lets only
configure the env variable if TEXT_BASE is defined.

Signed-off-by: Stefan Roese <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Bin Meng <[email protected]>
Cc: Tom Rini <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Reviewed-by: Bin Meng <[email protected]>