BeagleBoneBlackPkg: Cleanup DEC, DSC

Remove unused sections.

Signed-off-by: Varad Gautam <varadgautam@gmail.com>
BeagleBoneBlackPkg: Fix FD Load Address

MLO places u-boot at CONFIG_SYS_TEXT_BASE=0x80800000. Load FD at the
same address.

DxeCore now loads.

Closes http://sourceforge.net/p/edk2/mailman/edk2-devel/thread/0877601216922E4B83A7129715B5DA2BAC509763C8%40GEORGE.Emea.Arm.com/#msg32648571

Signed-off-by: Varad Gautam <varadgautam@gmail.com>
BeagleBoneBlackPkg: Implement TimerLib

Add TimerLib for use in PEI and DXE phases.

Signed-off-by: Varad Gautam <varadgautam@gmail.com>