riscv: Fix guest RAM alloc size computation for RV32

Currently, we ensure that guest RAM alloc size is at least 2M for
THP which works well for RV64 but breaks hugepage support for RV32.
To fix this, we use 4M as hugepage size for RV32.

Fixes: 867159a7 ("riscv: Implement Guest/VM arch functions")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Link: https://lore.kernel.org/r/20230712163501.1769737-10-apatel@ventanamicro.com


Signed-off-by: Will Deacon <will@kernel.org>