mtd: rawnand: qcom: code reorganization for raw read

Make separate function to perform raw read for one codeword and
call this function multiple times for each codeword in case of
raw page read. This separate function will help in subsequent
patches related with erased codeword bitflip detection.

It will decrease throughput for raw page read. Raw page read
is used for debug purpose so it won't affect normal flash
operations.

Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>