board: freescale: p1_p2_rdb_pc: Remove I-flag from second L2 SRAM mapping

board: freescale: p1_p2_rdb_pc: Remove I-flag from second L2 SRAM mapping

U-Boot for initial L2 SRAM uses L2 memory-mapping mode and not L2 with
locked lines. P2020 reference manual about L2 memory-mapping mode says:

  Accesses to memory-mapped SRAM are cacheable only in the corresponding
  e500 L1 caches.

So there is no need to set Caching-Inhibit I-bit for second part of initial
L2 SRAM mapping in TLB entry. Remove it. First part of initial L2 SRAM
mapping already does not have I-bit set.

For more details see also:
https://lore.kernel.org/u-boot/20220508150844.qqxg452rs4wtf5bs@pali/

Signed-off-by: Pali Rohár <pali@kernel.org>