configs: at91: sama7g5ek: enable CONFIG_PHANDLE_CHECK_SEQ

CONFIG_PHANDLE_CHECK_SEQ will allow different sequence number for nodes
that have the same name, but they are different.
In sama7g5ek case, there are multiple 'i2c@600' nodes which are child
nodes of different parent 'flexcom' nodes.
These are different i2c busses even if the node is the same, and have to be
differentiated.
Without this config, the sequence number 0 is reused for two i2c busses, and
this is something that we have to avoid:

Looking for 'i2c' at 4704, name i2c@600
   - serial0, /ahb/apb/serial@e1824200
   - i2c0, /ahb/apb/flexcom@e181c000/i2c@600
Found seq 0
i2c_post_bind: i2c@600, seq=0
Looking for 'i2c' at 6236, name i2c@600
   - serial0, /ahb/apb/serial@e1824200
   - i2c0, /ahb/apb/flexcom@e181c000/i2c@600
Found seq 0
i2c_post_bind: i2c@600, seq=0

After this patch:

Looking for 'i2c' at 4704, name i2c@600
   - serial0, /ahb/apb/serial@e1824200
   - i2c0, /ahb/apb/flexcom@e181c000/i2c@600
   - i2c1, /ahb/apb/flexcom@e2818000/i2c@600
Found seq 1

Before the patch:
=> i2c bus
Bus 0:  i2c@600
Bus 0:  i2c@600  (active 0)
   52: eeprom@52, offset len 1, flags 0
   53: eeprom@53, offset len 1, flags 0
=>

After the patch:
=> i2c bus
Bus 0:  i2c@600
Bus 1:  i2c@600  (active 1)
   52: eeprom@52, offset len 1, flags 0
   53: eeprom@53, offset len 1, flags 0

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>