spi: spi-mtk-nor: add helper for checking prg mode ops

op checking/resizing logic for the newly added mtk_nor_spi_mem_prg is
more complicated. Add two helper functions for them:
mtk_nor_match_prg: check whether an op is supported by prg mode.
mtk_nor_adj_prg_size: adjust data size for mtk_nor_spi_mem_prg.

mtk_nor_match_prg isn't called yet because supports_op is currently
broken. It'll be used in the next fix commit.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
Link: https://lore.kernel.org/r/20200924152730.733243-3-gch981213@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>