mtd: rawnand: stm32_fmc2: increase DMA completion timeouts

When the system is overloaded, DMA data transfer completion occurs after
100ms. Increase the timeouts to let it the time to complete.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>