For these systems there is SPI in bitbang and/or hardware version:

• noforth, SPI for noForth including examples, OLED, Flash memory, etc.
• mecrisp-quintus, SPI for mecrisp including a BME280 & SD-card example

Read a character using SPI from a W25Q64 external Flash memory

The hardware user manual of the GD32F103 may be used to get some additional info on the GD32VF103 chips!
But take care the site is by current browser standards seen as a security risk!