feat(plat/xilinx/zynqmp): optimization on pinctrl_functions

Optimizing the pinctrl_functions structure. Remove the pointer to
array of u16 type which consumes a lot of memory (64bits pointer to
array + 16B for END_OF_GROUPS + almost useless 8bits on every entry
which is the same for every group) and add two new members of type
u16 and u8 with the name called group_base and group_size
respectively.

The group_base member contains the base value of pinctrl group whereas
the group_size member contains the total number of groups requested
from the pinctrl function.

Overall, it saves around ~2KB of RAM and ~0.7KB of code memory.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Ronak Jain <ronak.jain@xilinx.com>
Change-Id: I79b761b45df350d390fa344d411b340d9b2f13ac