dw_dmac: Change value of DWC_MAX_COUNT to 4095.

Every descriptor can transfer a maximum count of 4095 (12 bits, in control reg),
So we must have DWC_MAX_COUNT as 4095 instead of 2048.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>