accel/tcg: Inline tb_flush_jmp_cache

This function has two users, who use it incompatibly.
In tlb_flush_page_by_mmuidx_async_0, when flushing a
single page, we need to flush exactly two pages.
In tlb_flush_range_by_mmuidx_async_0, when flushing a
range of pages, we need to flush N+1 pages.

This avoids double-flushing of jmp cache pages in a range.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>