firmware: coreboot: Remap RAM with memremap() instead of ioremap()

This is all system memory, so we shouldn't be mapping this all with
ioremap() as these aren't I/O regions. Instead, they're memory regions
so we should use memremap(). Pick MEMREMAP_WB so we can map memory from
RAM directly if that's possible, otherwise it falls back to
ioremap_cache() like is being done here already. This also nicely
silences the sparse warnings in this code and reduces the need to copy
anything around anymore.

Cc: Wei-Ning Huang <wnhuang@chromium.org>
Cc: Julius Werner <jwerner@chromium.org>
Cc: Brian Norris <briannorris@chromium.org>
Cc: Samuel Holland <samuel@sholland.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>