spi: airoha: avoid usage of flash specific parameters

spi: airoha: avoid usage of flash specific parameters

The spinand driver do 3 type of dirmap requests:
 * read/write whole flash page without oob
   (offs = 0, len = page_size)
 * read/write whole flash page including oob
   (offs = 0, len = page_size + oob_size)
 * read/write oob area only
   (offs = page_size, len = oob_size)

The trick is:
 * read/write a single "sector"
 * set a custom sector size equal to offs + len. It's a bit safer to
   round up "sector size" value 64.
 * set the transfer length equal to custom sector size

And it works!

Thus we can find all data directly from dirmap request, so flash specific
parameters is not needed anymore. Also
 * airoha_snand_nfi_config(),
 * airoha_snand_nfi_setup()
functions becomes unnecessary.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>