drm/i915/icl: Implement HSDIV_RATIO of MG_CLKTOP2_HSCLKCTL_PORT reg as separate divid...

drm/i915/icl: Implement HSDIV_RATIO of MG_CLKTOP2_HSCLKCTL_PORT reg as separate divider value defines

The register value of Divider Ratio for high speed divider
(hsdiv_ratio) in MG_CLKTOP2_HSCLKCTL_PORT register is not same as the
actual numerical value of the divider. So this patch implements
separate divider value defines for that field.
icl_mg_pll_find_divisors() can use these defines instead of magic
register values.

The new defines are going to be used in the next patch.

v2 (from Paulo):
 * Rebase.
 * Make it look a little more like the rest of our code.
v3 (from Paulo):
 * Make hsdiv u32 now that it's a bit field (José).

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Suggested-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180817215209.29133-1-paulo.r.zanoni@intel.com