mtd: nand: add a function to count bad blocks before a given offset

In case of FIP, the offsets given in the FIP header are relative. If bad
blocks are found between the FIP base address and this offset, the offset
should be updated taking care of the bad blocks.

Change-Id: I96fefabb583b3d030ab05191bae7d45cfeefe341
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/175511


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Lionel DEBIEVE <lionel.debieve@st.com>