riscv: Fix set_direct_map_default_noflush() to reset _PAGE_EXEC

riscv: Fix set_direct_map_default_noflush() to reset _PAGE_EXEC

[ Upstream commit b8b2711336f03ece539de61479d6ffc44fb603d3 ]

When resetting the linear mapping permissions, we must make sure that we
clear the X bit so that do not end up with WX mappings (since we set
PAGE_KERNEL).

Fixes: 395a21ff859c ("riscv: add ARCH_HAS_SET_DIRECT_MAP support")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20231213134027.155327-3-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>