Remove hard-coded CDMA roaming mode restrictions.

Prior to this, the CDMA roaming mode (from the "System select" setting) is
vetted against a hard-coded list of two acceptable values (CDMA_RM_HOME:0
and CDMA_RM_ANY:2).  This commit instead vets against the
cdma_system_select_values list, which contains those two values by default,
but may be overridden on a per-device basis.

For motivation, epicmtd in stock Gingerbread doesn't use CDMA_RM_ANY:2, but
values 5-8 to select between automatic domestic, international, both, and
no roaming.  Without this, roaming is unintentionally disabled anytime the
"Mobile networks" setting screen is opened.

From CM9: I589c660fe3a1b9920cecfc7e6dc044f3f722fbb2

Change-Id: I6611822822f32cd132a1794e7ca11bf5f751994d