riscv/mm: add arch hook arch_clear_hugepage_flags

riscv/mm: add arch hook arch_clear_hugepage_flags

With the PG_arch_1 we keep track if the page's data cache is clean,
architecture rely on this property to treat new pages as dirty with
respect to the data cache and perform the flushing before mapping the pages
into userspace.

This patch adds a new architecture hook, arch_clear_hugepage_flags,so that
architectures which rely on the page flags being in a particular state for
fresh allocations can adjust the flags accordingly when a page is freed
into the pool.

Fixes: 9e953cda5cdf ("riscv: Introduce huge page support for 32/64bit kernel")
Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
Link: https://lore.kernel.org/r/20221024094725.3054311-3-tongtiangen@huawei.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>