1) fixed SPI_read_status: added check for flash busy flag in matrix mode
2) fixed SPI_page_program: enable write before writing data to SPI FIFO
3) SPI flash ROM funcs replacement is controlled via menuconfig option
* Erase range operations allow preemption after each block or sector.
* Write operations allow preemption every 8KB of data.
* Reado operations allow preemption every 16KB of data.