[PATCH v2] mtd: spinand: cache the last read page to avoid redundant SPI operations

[Zongzhen Feng]

Hi Miquèl,

Thanks for the review. v3 has been sent to address the two issues
found by Sashiko:

- Invalidate cache when the bounce buffer is overwritten by
  non-cacheable reads (RAW, continuous, or OOB-only) to prevent
  serving stale data on subsequent cache hits.

- Invalidate cache on uncorrectable ECC errors to prevent
  subsequent reads from bypassing ECC checks and silently
  returning corrupted data.

Regards,
Zongzhen Feng