riscv: Fix Stage2 SV32 page table walk

As-per RISC-V H-Extension v0.5 draft, the Stage2 SV32 page table has
12bits of VPN[1] and 10bits of VPN[0]. The additional 2bits in VPN[1]
is required to handle the 34bit intermediate physical address coming
from Stage1 SV32 page table. The 12bits of VPN[1] implies that Stage2
SV32 level-0 page table will be 16KB in size with total 4096 enteries
where each entry maps 4MB of memory (same as Stage1 SV32 page table).

The get_physical_address() function is broken for Stage2 SV32 level-0
page table because it incorrectly computes output physical address for
Stage2 SV32 level-0 page table entry.

The root cause of the issue is that get_physical_address() uses the
"widened" variable to compute level-0 physical address mapping which
changes level-0 mapping size (instead of 4MB). We should use the
"widened" variable only for computing index of Stage2 SV32 level-0
page table.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20200330082724.120444-1-anup.patel@wdc.com
Message-Id: <20200330082724.120444-1-anup.patel@wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>