1) Please refer to the QorIQ LS1021A Reference Manual, 4.4.7 Clocking to select a clocking mode.
2) The question is not clear.
3) Usage of INA220 is not a must.
4) External 125 MHz reference clock (ECn_GTX_CLK125) is needed if RGMII interface is used.
5) Please refer to the QorIQ LS1021A Reference Manual, Table 33-2. Supported SerDes options, column "Per lane PLL mapping":
"1" corresponds to the PLL1
"2" corresponds to the PLL2
Example:
SRDS_PRTCL_S1 = 0x10
Per lane PLL mapping: 1211
Lanes A, C, D - PLL1
Lane B - PLL2
If PLLn is not used then it has to be powered down and corresponding reference clock is not needed.