drm/i915/glk: Reuse broxton code for geminilake

Geminilake is mostly backwards compatible with broxton, so change most
of the IS_BROXTON() checks to IS_GEN9_LP(). Differences between the
platforms will be implemented in follow-up patches.

v2: Don't reuse broxton's path in intel_update_max_cdclk().
    Don't set plane count as in broxton.

v3: Rebase

v4: Include the check intel_bios_is_port_hpd_inverted().
    Commit message.

v5: Leave i915_dmc_info() out; glk's csr version != bxt's. (Rodrigo)

v6: Rebase.

v7: Convert a few mode IS_BROXTON() occurances in pps, ddi, dsi and pll
    code. (Rodrigo)

v8: Squash a couple of DDI patches with more conversions. (Rodrigo)

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480667037-11215-2-git-send-email-ander.conselvan.de.oliveira@intel.com