bcma: move parallel flash support to separated file

This follows the way of handling other flashes and cleans code a bit. As
next task we will want to move flash code to ChipCommon driver as:
1) Flash controllers are accesible using ChipCommon registers
2) This code isn't MIPS specific
This change prepares bcma for that.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>