armv8: layerscape: Fix TF-A DRAM reservation with empty banks

The TF-A DRAM bank setup currently assumes that the number of
banks reported by TF-A matches the number of entries available in
gd->bd->bi_dram[].  Limit the loop by CONFIG_NR_DRAM_BANKS so that
a platform with fewer configured DRAM banks does not write past the
array.

The reserved RAM setup also checks higher DRAM banks before falling
back to bank 0.  When a higher bank is empty and board_reserve_ram_top()
returns 0, the old test succeeds for a zero-sized bank.  This can set
gd->arch.resv_ram to 0.

On systems with CONFIG_GIC_V3_ITS this value is later used by
ls_gic_rd_tables_init() to place the GIC LPI tables:

  gd->arch.resv_ram - GIC_LPI_SIZE

If gd->arch.resv_ram is 0, the subtraction underflows and the GIC LPI
tables are placed at an invalid high address.

Skip empty banks when selecting the reserved RAM area and fail GIC LPI
table setup if no reserved RAM address was established.

This fixes LS1028A systems with 2 GiB of RAM, where TF-A reports only
one populated DRAM bank.

Tested on an LS1028ARDB with TF-A modified to report 2 GiB of RAM, and
on a custom LS1028A-based board equipped with 2 GiB of RAM.

Signed-off-by: Patryk Biel <[email protected]>
Signed-off-by: Peng Fan <[email protected]>

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