Fix printing of make targets, simplify Makefile

Make printing the "board names" more useful. So far, we would get
output like this;

$ ./MAKEALL P2020RDB P2020RDB_NAND P2020RDB_SDCARD P2020RDB_SPIFLASH
Configuring for P1_P2_RDB board...
   text    data     bss     dec     hex filename
 342612   32656  265212  640480   9c5e0 /work/wd/tmp-ppc/u-boot
Configuring for P1_P2_RDB board...
   text    data     bss     dec     hex filename
 343160   32704  265212  641076   9c834 /work/wd/tmp-ppc/u-boot
Configuring for P1_P2_RDB board...
   text    data     bss     dec     hex filename
 341908   32620  265212  639740   9c2fc /work/wd/tmp-ppc/u-boot
Configuring for P1_P2_RDB board...
   text    data     bss     dec     hex filename
 341908   32620  265212  639740   9c2fc /work/wd/tmp-ppc/u-boot

For all build targets the same board name would be printed, which
makes is often pretty difficult to find out which exact build target
caused problems. With this commit, the real make target name gets
printed instead, which is way more useful:

$ ./MAKEALL P2020RDB P2020RDB_NAND P2020RDB_SDCARD P2020RDB_SPIFLASH
Configuring for P2020RDB board...
   text    data     bss     dec     hex filename
 342612   32656  265212  640480   9c5e0 /work/wd/tmp-ppc/u-boot
Configuring for P2020RDB_NAND board...
   text    data     bss     dec     hex filename
 343160   32704  265212  641076   9c834 /work/wd/tmp-ppc/u-boot
Configuring for P2020RDB_SDCARD board...
   text    data     bss     dec     hex filename
 341908   32620  265212  639740   9c2fc /work/wd/tmp-ppc/u-boot
Configuring for P2020RDB_SPIFLASH board...
   text    data     bss     dec     hex filename
 341908   32620  265212  639740   9c2fc /work/wd/tmp-ppc/u-boot

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Detlev Zundel <dzu@denx.de>
Tested-by: Thomas Chou <thomas@wytron.com.tw>