config: Use additional man page support from util-macros 1.8

config: Use additional man page support from util-macros 1.8

Use MAN_SUBST now supplied in XORG_MANPAGE_SECTIONS
The value of MAN_SUBST is the same for all X.Org packages.

Use AC_PROG_SED now supplied by XORG_DEFAULT_OPTIONS
The existing statement can now be removed from the configuration file.

Use automake provided $(AM_V_GEN) and XORG_DEFAULT_OPTIONS provided $(SED)
Enables silent rule and use platform appropriate version of sed.

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>