Optimize ResourceClientBits() funtion

The LimitClients variable could be set in three different places: os/osinit.c, os/utils.c and hw/xfree86/common/xf86Config.c.
In these places, it checks if the variable is 64, 128, 256, 512, 1024 or 2048.
So we can optimize ResourceClientBits() to start looking in 7th bit (value of 64).
Another optimization is to avoid calling repeatedly the ResourceClientBits() function as the variable LimitClients is set only once.
So call ResourceClientBits() only when setting LimitClients.
The macros defined in include/resource.h is replaced by global variables and calculated together LimitClients too avoiding to recalculate every time is used.
It can lead to a speedup of ~1% in xserver.
4 jobs for resourceclientbits in 7 minutes and 9 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Docker Image
passed debian-testing #2304808

00:00:32

 
  Build And Test
passed autotools #2304809

00:06:36

passed meson #2304810

00:01:02

passed meson-noglamor #2304811

00:00:47