BaseTools GenFw: Fix the issue to update the wrong size as SectionSize

BaseTools GenFw: Fix the issue to update the wrong size as SectionSize

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1603
CLANG9 generated PE image exposes below two issues.
1. SectionSize is used to copy PE section data. It should be smaller than
section raw size.
2. The real data is required to be copied. So, copy the min size of
VirtualSize and SizeOfRawData.

Signed-off-by: Liming Gao <liming.gao@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>